Thermographic Survey at Hagia Sophia: Main Arches, Pendentives and Tympana

International Journal of Architectural Heritage Conservation, Analysis, and Restoration ISSN: 1558-3058 (Print) 1558-3066 (Online) Journal homepage: https://www.tandfonline.com/loi/uarc20 Thermographic Survey at Hagia Sophia: Main Arches, Pendentives and Tympana Marco Cappa, Daniela De Angelis, Alessandra Pecci, Luis Barba, Murat Cura, Gino Mirocle Crisci, Jorge Blancas, Hasan Bora Yavuz & Domenico Miriello To cite this article: Marco Cappa, Daniela De Angelis, Alessandra Pecci, Luis Barba, Murat Cura, Gino Mirocle Crisci, Jorge Blancas, Hasan Bora Yavuz & Domenico Miriello (2016) Thermographic Survey at Hagia Sophia: Main Arches, Pendentives and Tympana, International Journal of Architectural Heritage, 10:6, 726-734, DOI: 10.1080/15583058.2015.1104400 To link to this article: https://doi.org/10.1080/15583058.2015.1104400 Accepted author version posted online: 02 Mar 2016. Published online: 02 Mar 2016. Submit your article to this journal Article views: 314 View Crossmark data Citing articles: 2 View citing articles Full Terms & Conditions of access and use can be found at https://www.tandfonline.com/action/journalInformation?journalCode=uarc20 INTERNATIONAL JOURNAL OF ARCHITECTURAL HERITAGE 2016, VOL. 10, NO. 6, 726–734 http://dx.doi.org/10.1080/15583058.2015.1104400 Thermographic Survey at Hagia Sophia: Main Arches, Pendentives and Tympana Marco Cappaa,b, Daniela De Angelisb, Alessandra Pecci a,c, Luis Barbad, Murat Curaa, Gino Mirocle Criscia, Jorge Blancasc, Hasan Bora Yavuze, and Domenico Mirielloa a Department of Biology, Ecology and Earth Sciences (DiBest), University of Calabria, Rende, Italy; bRestructura – Surveys for Cultural Heritage, Cosenza, Italy; cERAAUB, Departament de Història i Arqueologia, Universitat de Barcelona, Barcelona, Spain; dInstitute of Anthropological Research (IIA), National Autonomous University of Mexico, Mexico City, Mexico; eFreelance Surveying Engineer, Laser Scanning Expert, Istanbul, Turkey ABSTRACT ARTICLE HISTORY Hagia Sophia is one of the oldest and most complex existing monuments. Many unanswered questions are still open on the historical and constructive evolution of this monument. The boundaries between the different construction phases and the details of the masonry and materials used in the various phases are still not defined with precision. The thermographic survey, carried out inside the monument, made it possible to answer some of these questions by specifying the exact location of the past interventions and the variability of the materials employed allowing a better understanding of the constructive history of the monument. The technique was applied at a great distance and in normal environmental conditions, taking advantage of the high thermal sensitivity of the instrumentation. The results achieved confirm the validity of the technique in the study of ancient buildings. Received 10 January 2015 Accepted 2 October 2015 1. Introduction IR thermography is an imaging diagnostic technique that was developed in parallel with the digital technological evolution of the 20th century. The development of instruments with high thermal sensibility allows the investigation of wide surfaces, even from a long distance. The technique, developed for military purposes, was later used for the study of buildings and cultural heritage (Gomez-Heras et al., 2010; Grinzato et al., 2002; Imposa, 2010; Kordatos et al., 2013; Maldague, 2001). The first use of thermography in these fields mainly involved the identification of humidity infiltrations, detachments, and cavities. Other applications have proposed the identification of anomalies in building processes, the verification of the conservation state, and evaluation of the presence of different materials due to restorations (Avdelidis, Moropoulou, and Delegou 2004; Cura 2010; Meola 2007). The thermographic investigations carried out at Hagia Sophia are very few and have often focused on limited portions of the building. First investigations were carried out in 2000, and are part of a work which involved a series of analyses of building materials and of some architectural surfaces. In particular, the thermographic investigations focused KEYWORDS Ayasofya; constructive evolution; Hagia Sophia; penditives; thermography; tympana on characteristics of absorption of water by the mortars (Moropoulou and Polikreti 2010). Previous thermographic survey at Hagia Sophia was also used for the identification of materials and mosaics, and the evaluation of the conservation state of the materials of the northeast area of the dome (Avdelidis and Moropoulou 2004; Avdelidis, Moropoulou, and Delegou 2004; Moropoulou et al. 2013). In 2002, thermographic investigations involved the northern semi-dome, and allowed the individuation of some alterations present on the surface (Cura 2010). At Hagia Sophia the authors experimented the use of thermography as a tool to study constructive characteristics, such as the presence of different materials and their organization, related to different constructive phases. There are still many open issues related to the location of the limits of the numerous interventions, repair, or reconstruction activities carried out on the monument, as well as issues related to which materials were used to carry out these interventions. The hypotheses that have so far been proposed regarding these problems have not been supported by diagnostic investigations. We, herewith, present the results of the thermographic campaign carried out in April 2013, which had the objective CONTACT Marco Cappa, PhD m.cappa@restructuraweb.com Department of Biology, Ecology and Earth Sciences (DiBest), University of Calabria, Rende (CS), Italy; Restructura – Surveys for Cultural Heritage, Cosenza, Italy. Color versions of one or more of the figures in this article can be found online at www.tandfonline.com/uarc. © 2016 Taylor & Francis INTERNATIONAL JOURNAL OF ARCHITECTURAL HERITAGE of helping to solve some of these open issues. The first step was the identification of the possible anomalies of the constructive tissue which are mentioned in literature (Mainstone 2009), followed by the identification of discontinuities between the various materials present in the monument, thus determining the exact location of the various phases of construction. In particular, we present the results of the thermal investigation carried out on the main arches, the pendentives and the tympana of the monument. 2. Constructive evolution The history of Hagia Sophia is particularly dense. It can be summarized in two major time intervals corresponding to the same number of construction phases (Mainstone 2009; Mango 1999). (1) From the 6th–14th centuries. After the fire during the Nika revolt against the Emperor Justinian I, which caused the destruction of Hagia Sophia in AD 532, Emperor Justinian I immediately began the construction of a new building. It was opened on December 27, 537 AD. It was built by the architect Isidore of Miletus and the physical and mathematician Anthemius of Tralles. The earthquakes of 553 and 557 caused cracks which led to the collapse of the dome on the May 7, 558 AD. Isidore the Younger was in charge of the reconstruction work. He chose to use lighter materials than those previously used, and changed the profile of the dome. Later, the damage caused by the earthquake of 869 was repaired by the Byzantine emperor Basil II and the Armenian architect Trdat. The church was reopened in May 994. In 1346, there was a collapse of some structural elements in the east side, which led to the closure of the building until 1354, when the repairs done by the architects Astras and Peralta were finished. (2) From the 15th–19th century. Shortly after the conquest of Constantinople in 1453, Mehmed II converted Hagia Sophia into the Ayasofya Mosque. He ordered the construction of the first minaret (the south-east one) and the plastering of the wall mosaics. Under the Sultanate of Selim and under the guidance of the Ottoman architect Mimar Sinan strengthening works were carried out, and two minarets and the mausoleum of the Sultan were built. One of the largest and most complete restoration works of Ayasofya was ordered by Sultan Abdul Mejid I, and completed between 1847 and 1849, under the direction of the architect Fossati. The dome was consolidated and the pillars 727 strengthened and straightened. Moreover, steel chains were inserted around the base of the dome, and the surviving Byzantine mosaics were discovered and covered with a new layer of plaster, while old chandeliers were replaced by new ones. In the upper columns, four circular medallions, painted by calligrapher Kazasker İzzed Effendi, were hung. On July 13, 1849, at the end of the restoration, the mosque was reopened for worship. In 1934, the building was transformed into a museum by Mustafa Kemal Atatürk (Necipoglu 1992). Since then, several studies have been conducted and there have been numerous restoration, reconstruction and consolidation works, many of which are still in progress. The monument today shows some structural deformations. These affect the arches, vaults, dome, and colonnades and show a state of instability that has accompanied it for a long time. The nave, which creates a space of about 30 m wide by 80 m long, is bordered by a series of piers and columns that separate it from the side corridors on the ground floor and the upper gallery. The nave, which ends with an apse in the eastern side, is covered by the dome, by two half-domes (Figure 1, letter G) and four exedras (Figure 1, letter F). The pendentives are located at the corners of the main dome (Figure 1), which has a maximum diameter of 31.24 m, and it is 55.6 m above the soil surface (Erdik and Croci 2010; Van Nice, 1965). The pendentives (Figure 1, point H) delimit the principal arches (Figure 1, letter B) and, together with the latter, they support the dome and distribute the weight of the dome to the pillars. Secondary arches Figure 1. Primary and secondary constructive system of the monument (from Mainstone, 2009). © Mainstone et al. Reproduced by permission of Mainstone et al. Permission to reuse must be obtained from the rightsholder. 728 M. CAPPA ET AL. are placed under the system of the principal arches (Figure 1, letter A). The walls under the upper arches in the northern and southern sides form the tympana. These walls are not visible from the interior, but only from the exterior of the monument. The materials used to build the dome, the pendentives, the half-domes, and the tympana are mainly bricks. In the Narratio de structura temple S. Sophiae the bricks used for the main arches and the dome came from Rhodes Island and they are 40–50 mm thick. The document also mentioned that the mortar is made of lime, sand, and brick fragments, and that the thickness of the mortar layers is 50–60 mm, wider than that of the bricks (Preger 1998). The base of the dome is made of marble blocks, while the dome itself is made of bricks. The reconstruction of the dome (Figure 2) carried out in the 6th century AD involved raising the dome 20 byzantine feet (approx 6.24 m). In the 10th century, a portion in the western side of the dome was reconstructed by the architect Trdat and, in the 14th century, a portion in the eastern side was rebuilt by the architects Astras and Peralta. Moreover, isolated interventions were carried out in the 10th century in the upper part of the northeast pendentive (Mainstone 2009). The pendentives are the triangular portions of the sphere that connects the quadrangular base of the dome with the hemisphere of the dome itself. Their history is related to that of the dome. The main interventions which have led to the current situation are those that interested the dome between the 6th and the 14th centuries. Figure 2. Map of the dome with the limits of the reconstructions (from Mainstone, 2009). © Mainstone et al. Reproduced by permission of Mainstone et al. Permission to reuse must be obtained from the rightsholder. The arches at Hagia Sophia are on two levels: the lower arches (Figure 1, letter A) supporting the tympana, and the upper arches (Figure 1, letter B) supporting the dome. The main interventions in which they were involved are: the reconstruction of the 6th century, after the collapse of the dome, of the eastern arch and the modifications of the south and north arches; ● the reconstruction of the western arch in the 10th century; and ● the collapse of the main arch in the 14th century and the following reconstruction. ● The upper and lower north and south arches have never been reconstructed and are symmetrical with different heights (Mainstone 2009). The tympana have suffered several reconstruction interventions due to the fragility of the colonnades that support them. They were completely re-built in the 6th and 10th century after the colonnades were destroyed. In the 14th century, the openings of the windows were reduced to try to give more stability to the walls. The main semi-domes have also been repaired following the events that characterized the history of the east and west portions of the building. The earthquake of the 6th century produced fractures in the east semi-dome. In the 10th and 14th century the main semi-domes were reconstructed at the same time as the dome. 3. Methodology The thermografic surveys were carried out with an IR thermocamera with an uncooled microbolometer detector, model SC640, produced by Flir Systems AB, with a 24° lent and electronic zoom 8x. The thermocamera has an IR resolution of 640 x 480, a thermic sensibility of 30 mK at 30°C with a frequency of image of 30 Hz. The view field is 24° x 18° (FOV) with a minimum focusing distance of 0.3 m. The maximum distance for a good acquisition of data depends on the differences of temperature between the object and the environment. At Hagia Sophia the maximum distance between the camera and the objects investigated has reached even more than 25 m. The accuracy of the instrument is maintained between ±1°C and ±1% in a temperature range reaching 120°C. The camera has a spectral field between 7.5 and 13 µm. The instrument also has an incorporated digital camera with a resolution of 3.2 megapixels, and it has an SD memory slot, in which thermal and digital images, as well as thermal videos are saved. INTERNATIONAL JOURNAL OF ARCHITECTURAL HERITAGE The software used to elaborate thermographic images is ThermaCAM Researcher Pro 2.10 and Tool+ produced by Flir Systems AB. The following protocol was applied for the thermographic research: ● ● ● ● ● preliminary identification of the points of the station; measurement of environmental conditions (parameters of room temperature, reflected temperature, relative humidity, and distances from the objects); insertion of environmental parameters and identification of emissivity parameter; identification of the areas to be inspected, acquisition of thermal images and the corresponding digital images; and post-processing data, analyses of thermograms and building thermal image mosaics. During the entire work, passive processes were used and, therefore, no heat sources were used in support of the thermographic surveys. The temperatures acquired were analyzed qualitatively evaluating the differences in temperature inside the individual thermal images. As previously stated, this work presents the results of the thermal study carried out on the main arches, the pendentives, and the tympana of the monument. 4. Results 4.1. Pendentives Following Mainstone (2009), all the pendentives were built using 40 mm thick bricks, interspaced with layers of lime mortar mixed with sand, with a greater thickness than that of the bricks (50–60 mm). The fact that the mortar is thicker than the bricks is probably due to the necessity of making a curvature in the pendentives that respected the geometric lines of the sphere. The thermographic inspections show the presence in the pendentives of materials that are different by type and size. Moreover, they allow us to identify some important differences among the four pendentives, thus testifying the presence of various construction phases and constructive methods used over the centuries. The thermographic investigation of the south-east pendentive (Figure 3) shows that the building materials are organized with regularity, following ordered lines of materials with different thermal characteristics. The material and typological continuity detected demonstrate a willingness to make the pendentives and the arches above the tympana more clamped, thus, more resistant to stress. 729 The choice of posing these horizontal and substantially equidistant lines of materials is associated with the fact that they are linked to the main southern arch. The thermal analysis shows that there are five lines in the pendentive (four of which correspond to those of the main arch in the south side). The thickness of these lines is almost the same. This type of masonry probably corresponds to the intervention of Astras and Peralta, which took place in the 14th century AD, after the earthquake of 1343 (Mainstone 2009). In the pendentive in the northeast side (Figure 4), located on the right of the apse, a geometric distortion is particularly evident already to the naked eye. This distortion testifies a junction between two non-contemporaneous parts. In fact, this point, which is visible to the naked eye at the top, shows the attempt to connect two parts that were built in different periods. The eastern area shows a portion of the masonry with the same lines detected in the south-east pendentive. In this area, the thermographic inspection shows the presence of a discontinuity in the materials used. The thermography shows a vertical strip of lighter color (Figure 4, point c) that testifies the point where the two masonries were joined together and there is an interruption of the horizontal lines of the east portion of the pendentive. In the north part, there is a different type of construction, characterized by the use of disordered and heterogeneous materials. Here it is not easy to recognize the restorations carried out in the 10th century reported by Mainstone (2009). Four lines can be clearly identified in the eastern portion. The lower ones are integrated at several points to the adjacent parts, but they tend to diverge from the original line. In this case, although the thickness of the lines of materials is similar to the previous pendentive, they are not equidistant, and there is no correspondence between the lines of the eastern part and the adjacent arch. Also in the northwest pendentive (Figure 5), it is possible to detect—through a thermographic inspection —lines of different materials. However, in this pendentive, differently from the previous one, there are only two lines. In the bordering part with the northern tympanum, there is a discontinuity in the upper line (Figure 5, point d). This discontinuity could indicate the boundary between the part that was re-built in the 6th century and the one that was built in the 10th century (Mainstone 2009). The thickness of these lines is less constant and smaller than the previous ones, probably because blocks of different size were used. The upper arch of the northern tympanum, bordering the pendentive, does not show any lines and, therefore, there is no correspondence between the lines of the pendentive and the upper arch. 730 M. CAPPA ET AL. Figure 3. Photo and thermal image of the south-east pendentive taken from the apse. Figure 4. Photo and thermal image of the north-east pendentive taken from the apse. Figure 5. Photo and thermal image of the north-west pendentive taken from the center of the nave. In the arch in the west side, although there are lines with different materials, they are not built with the same constructive order as the southeast pendentive, and the thickness of these lines is smaller than those in the adjacent pendentive. The other materials used show thermal homogeneity. The decorative surfaces of the south-west pendentive (Figure 6) have been recently restored. This pendentive is different from all the others. In particular, it is possible to differentiate three areas. The upper one (Figure 6 point e), at the edge of the south tympanum, does not show any lines and it is homogeneous in its material composition. Here, there are holes visible even to the naked eye. Thanks to the thermographic analysis, it is possible to understand that these holes only cross the wall of the pendentive, but do not cross the external wall. In fact, they appear of a dark color in the thermographic image (which means they are colder). If they had crossed the external wall they would have appeared of a lighter color (yellow/white), due to the higher temperature of the outside. INTERNATIONAL JOURNAL OF ARCHITECTURAL HERITAGE 731 Figure 6. Thermal image of the south-west pendentive taken from the center of the nave, which shows the three areas with important constructive differences. In the lower part of the pendentive (Figure 6, point f) the four almost equidistant thick lines are interrupted in the middle of the area. The part of the pendentive that is adjacent to the western arch (Figure 6, point g) is similar to the northwest pendentive. In fact, there are only two lines with irregular thicknesses, which is caused, also in this case, by the use of similar materials but with different thicknesses. Another singularity in this pendentive is the tendency of the line to be directed upward. In fact, the line is not parallel to the edge of the dome, but has an inclination towards the arch to the west. A similar situation can be observed, although to a lesser extent, in the northwest pendentive. The lines of the pendentives do not continue in the arches adjacent to the west and above the south tympana. 4.2. Main arches The arches located in the area corresponding to the apse and the main entrance (Figure 1, letter C) have undergone several reconstructions. From the thermal images this is evident because it is possible to observe that the arch to the west (Figure 9, point m) shows thin lines of different materials which are almost equidistant. However, these lines are not connected to those of the adjacent pendentives. In addition, these lines are thinner than the lines of the pendentives. In the central portion of the arch in the east side, it is possible to observe the presence of three lines. This could be interpreted as the result of an attempt to intensify the lines near the keystone of the arch. The arch in the east side, which delimits the central nave and the apse, was most recently rebuilt (Mainstone 2009). The thermographic inspection shows that this arch has the same characteristics as the arch in the west side. In the lower part of the arch, both in the north and south side, it is possible to observe the presence of blocks of material with different widths (Figure 3, points a and Figure 4, points b). Due to the fact that this material has similar thermal parameters in the northeast and southeast pendentives, it is possible to identify them as stone blocks. The northern and southern main arches (Figure 1, letter B) only partly belong to an older period than the other main arches. In fact, they were probably rebuilt in the 6th century (Figure 2) (Mainstone 2009). In the southern arch, the reconstructions that affected the portions bordering the pendentive in the eastern side are more evident. In Figure 8, in particular, it is possible to observe that the constructive technique of the eastern pendentive extends the lines to the arch. Instead, the central and western portions of the arch, do not show any lines, and they are composed of the same material up to the junction with the underlying pillar in the west side. Due to the thermal homogeneity, this latter portion, may be considered as the oldest one with no alteration and, therefore, attributable to the 6th century. The main arch in north side has no evident thermal dishomogeneity. Only in certain points on the border with the northwest pendentive, some sporadic lines can be observed (Figure 9, point n). However, they have a reduced thickness, compared to the lines of the southern main arch. The rest of the arch (Figure 4) shows the same construction material. Most part of the latter, due to its homogeneity, can be attributed to the earliest period of reconstruction of the monument (6th century). 4.3. Tympana and secondary arches The materials with which the tympana were made, are bricks (Mainstone 2009). The thermographic survey allows the collection of information on the building of the tympana. In the north side tympanum (Figure 7), it is possible to distinguish the height and the characteristics of the secondary arch. In fact, at the top, a wide strip with a 732 M. CAPPA ET AL. Figure 7. Photo and thermal image of the north tympanum taken from the dome. Figure 8. Mosaic of the thermal images of the south tympanum. thermographic images allow the observation of the border between the windows and the tympana masonry under the plaster. The material added to realize the narrowing has lower temperature values than the surrounding materials. This is why they can be attributed to the use of a different material from the rest of the wall. Comparing the results of the thermography and the historical sources cited by Mainstone (2009), it is possible to assume that this filling was the result of the intervention directed by the architect Sinan. The analysis of the south Tympanum (Figure 8) shows similar evidence. In fact, both the bounding arch (Figure 8, points h and i) and the narrowing of the windows can be observed (Figure 8, point l). However, due to the different exposure of the wall, compared to the previous one, the quality of the thermal image, does not allow us to “see” the parts made of different materials with the same clarity. The same narrowings are visible in the windows that can be observed on the right of Figure 8 and in the secondary arch, on the left of the image. 5. Concluding remarks Figure 9. Mosaic of the thermal images of the main arc, tympanum, pendetives and dome from the nave. different temperature, is visible. Furthermore, it is also possible to identify the presence of an intervention aimed to narrowing the windows. As a matter of fact, the The thermographic study has allowed the identification of differences in the materials and construction methods that have marked the historical evolution of the monument. It allowed us to distinguish the areas that suffered reconstructions, and within them, the use of different materials. It has also contributed to the resolution of the issues related to the understanding of the exact limits of the reconstructions carried out during the centuries. In particular, the pendentives show differences that can be attributed to different periods of reconstruction. The distinction between the various construction typologies and materials used has allowed the identification of the boundaries between the different reconstructions. This analysis, together with the data reported in INTERNATIONAL JOURNAL OF ARCHITECTURAL HERITAGE literature (Mainstone 2009) suggest that the portions built in the 6th century show only bricks, while in the pendentives that were rebuilt after the 6th century, blocks of stone were added to the bricks. The parts rebuilt in the 10th century, on the other hand, show two thinner lines made of stone. The experience of the previous collapses, probably led the 14th century workers to build some parts of the monument augmenting the number of lines (which, here, are 5, instead of 4) placing them equidistantly, with a greater “constructive knowledge”. As for the main arches, thermography has allowed us to note that the ones in the northern and southern sides show many differences, which are closely related to the restoration works performed on the pendentives over the centuries. Only few of the portions of the arches show no lines and are, therefore, homogeneous, whereas the arches in the east and west side, show an occasional use of different materials. The thermographic inspections on the tympana and on the secondary arches have determined the width of the arch, which has the same depth of the masonry. They have also highlighted an intervention of narrowing of the windows, made using different materials from the one used in the corresponding masonry. Finally, this research has demonstrated the validity of the thermographic survey for the study of monuments. This technique has been able to provide additional information on the limits between the different construction phases, thus proving to be a valuable tool for testing the hypotheses proposed by literature without any kind of intervention on the monument. The technological evolution of the instruments provided, has allowed us to obtain a high sensibility of thermography and, therefore, achieve results even at a great distance, in non-ideal climatic conditions and without the use of artificial heat. Acknowledgment We thank all the staff and the direction of the Hagia Sophia Museum for their helpfulness and hospitality and the Ministry of Culture of Turkey for the granting of all permits necessary for the conduct of investigations inside the monument. The work is part of the joint research activity of the Department of Biology, Ecology and Earth Sciences (DiBest) of the University of Calabria and the Archaeological Prospection Laboratory of the Antropoligicas Institute of Research, National Autonomous University of Mexico (UNAM). It also part of the research for the Ph.D. thesis of Murat Cura titled “Costruzione di un database multimediale per un approccio multidisciplinare alla diagnostica di Santa Sofia”, which is being carried out at the Scuola di Dottorato “Archimede” in “Scienze, Tecnologie e Comunicazione” 733 (XVII Ciclo), in the frame work of the DiBEST – “Dipartimento di Biologia, Ecologia e Scienze della Terra”, University of Calabria (tutor: prof. Gino Mirocle Crisci, prof. Luis Barba, and dr. Domenico Miriello). All the thermal images were acquired by Marco Cappa (Level 2 Thermographer ISO 9712). Funding The research was conducted with the contribution of the Department of Biology, Ecology, Earth of the University of Calabria (Italy), which funded the entire campaign survey, and of Flir Systems Italy who provided the equipment for the thermographic investigations. ORCID Alessandra Pecci http://orcid.org/0000-0001-9649-1112 References Avdelidis, N. P., and A. Moropoulou. 2004. 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Karoglou, E. T. Delegou, K. C. Labropoulos, and N. S. Katsiotis. 2013. Diagnostics and protection of Hagia Sophia mosaics. Journal of Cultural Heritage 14 (3):133–139. doi:10.1016/j.culher.2013.01.006. Moropoulou, A., and K. Polikreti. 2010. Studying the Hagia Sofia structural materials: The conservation of the national technical University of Athens to the monument’s protection. Annual of Hagia Sofia Museum 13:155–76. Necipoglu, G. 1992. The life of an imperial monument: Hagia Sophia after Byzantinum. In Hagia Sophia from the age of Justinian to the present, ed. R. Mark, and A. Çakmak. New York, USA: Cambridge University Press. Preger, T. 1998. Scriptores originum Costantinopolitanarum. Leipzig, Germany: K.G. Saur Verlag. Van Nice, R. L. 1965. St Sofia in Istanbul: An architectural survey. Washington DC: The Dumbarton Oaks Center for Byzantines studies trustees for Harvard University. 

International Journal of Architectural Heritage Conservation, Analysis, and Restoration ISSN: 1558-3058 (Print) 1558-3066 (Online) Journal homepage: https://www.tandfonline.com/loi/uarc20 Thermographic Survey at Hagia Sophia: Main Arches, Pendentives and Tympana Marco Cappa, Daniela De Angelis, Alessandra Pecci, Luis Barba, Murat Cura, Gino Mirocle Crisci, Jorge Blancas, Hasan Bora Yavuz & Domenico Miriello To cite this article: Marco Cappa, Daniela De Angelis, Alessandra Pecci, Luis Barba, Murat Cura, Gino Mirocle Crisci, Jorge Blancas, Hasan Bora Yavuz & Domenico Miriello (2016) Thermographic Survey at Hagia Sophia: Main Arches, Pendentives and Tympana, International Journal of Architectural Heritage, 10:6, 726-734, DOI: 10.1080/15583058.2015.1104400 To link to this article: https://doi.org/10.1080/15583058.2015.1104400 Accepted author version posted online: 02 Mar 2016. Published online: 02 Mar 2016. Submit your article to this journal Article views: 314 View Crossmark data Citing articles: 2 View citing articles Full Terms & Conditions of access and use can be found at https://www.tandfonline.com/action/journalInformation?journalCode=uarc20 INTERNATIONAL JOURNAL OF ARCHITECTURAL HERITAGE 2016, VOL. 10, NO. 6, 726–734 http://dx.doi.org/10.1080/15583058.2015.1104400 Thermographic Survey at Hagia Sophia: Main Arches, Pendentives and Tympana Marco Cappaa,b, Daniela De Angelisb, Alessandra Pecci a,c, Luis Barbad, Murat Curaa, Gino Mirocle Criscia, Jorge Blancasc, Hasan Bora Yavuze, and Domenico Mirielloa a Department of Biology, Ecology and Earth Sciences (DiBest), University of Calabria, Rende, Italy; bRestructura – Surveys for Cultural Heritage, Cosenza, Italy; cERAAUB, Departament de Història i Arqueologia, Universitat de Barcelona, Barcelona, Spain; dInstitute of Anthropological Research (IIA), National Autonomous University of Mexico, Mexico City, Mexico; eFreelance Surveying Engineer, Laser Scanning Expert, Istanbul, Turkey ABSTRACT ARTICLE HISTORY Hagia Sophia is one of the oldest and most complex existing monuments. Many unanswered questions are still open on the historical and constructive evolution of this monument. The boundaries between the different construction phases and the details of the masonry and materials used in the various phases are still not defined with precision. The thermographic survey, carried out inside the monument, made it possible to answer some of these questions by specifying the exact location of the past interventions and the variability of the materials employed allowing a better understanding of the constructive history of the monument. The technique was applied at a great distance and in normal environmental conditions, taking advantage of the high thermal sensitivity of the instrumentation. The results achieved confirm the validity of the technique in the study of ancient buildings. Received 10 January 2015 Accepted 2 October 2015 1. Introduction IR thermography is an imaging diagnostic technique that was developed in parallel with the digital technological evolution of the 20th century. The development of instruments with high thermal sensibility allows the investigation of wide surfaces, even from a long distance. The technique, developed for military purposes, was later used for the study of buildings and cultural heritage (Gomez-Heras et al., 2010; Grinzato et al., 2002; Imposa, 2010; Kordatos et al., 2013; Maldague, 2001). The first use of thermography in these fields mainly involved the identification of humidity infiltrations, detachments, and cavities. Other applications have proposed the identification of anomalies in building processes, the verification of the conservation state, and evaluation of the presence of different materials due to restorations (Avdelidis, Moropoulou, and Delegou 2004; Cura 2010; Meola 2007). The thermographic investigations carried out at Hagia Sophia are very few and have often focused on limited portions of the building. First investigations were carried out in 2000, and are part of a work which involved a series of analyses of building materials and of some architectural surfaces. In particular, the thermographic investigations focused KEYWORDS Ayasofya; constructive evolution; Hagia Sophia; penditives; thermography; tympana on characteristics of absorption of water by the mortars (Moropoulou and Polikreti 2010). Previous thermographic survey at Hagia Sophia was also used for the identification of materials and mosaics, and the evaluation of the conservation state of the materials of the northeast area of the dome (Avdelidis and Moropoulou 2004; Avdelidis, Moropoulou, and Delegou 2004; Moropoulou et al. 2013). In 2002, thermographic investigations involved the northern semi-dome, and allowed the individuation of some alterations present on the surface (Cura 2010). At Hagia Sophia the authors experimented the use of thermography as a tool to study constructive characteristics, such as the presence of different materials and their organization, related to different constructive phases. There are still many open issues related to the location of the limits of the numerous interventions, repair, or reconstruction activities carried out on the monument, as well as issues related to which materials were used to carry out these interventions. The hypotheses that have so far been proposed regarding these problems have not been supported by diagnostic investigations. We, herewith, present the results of the thermographic campaign carried out in April 2013, which had the objective CONTACT Marco Cappa, PhD m.cappa@restructuraweb.com Department of Biology, Ecology and Earth Sciences (DiBest), University of Calabria, Rende (CS), Italy; Restructura – Surveys for Cultural Heritage, Cosenza, Italy. Color versions of one or more of the figures in this article can be found online at www.tandfonline.com/uarc. © 2016 Taylor & Francis INTERNATIONAL JOURNAL OF ARCHITECTURAL HERITAGE of helping to solve some of these open issues. The first step was the identification of the possible anomalies of the constructive tissue which are mentioned in literature (Mainstone 2009), followed by the identification of discontinuities between the various materials present in the monument, thus determining the exact location of the various phases of construction. In particular, we present the results of the thermal investigation carried out on the main arches, the pendentives and the tympana of the monument. 2. Constructive evolution The history of Hagia Sophia is particularly dense. It can be summarized in two major time intervals corresponding to the same number of construction phases (Mainstone 2009; Mango 1999). (1) From the 6th–14th centuries. After the fire during the Nika revolt against the Emperor Justinian I, which caused the destruction of Hagia Sophia in AD 532, Emperor Justinian I immediately began the construction of a new building. It was opened on December 27, 537 AD. It was built by the architect Isidore of Miletus and the physical and mathematician Anthemius of Tralles. The earthquakes of 553 and 557 caused cracks which led to the collapse of the dome on the May 7, 558 AD. Isidore the Younger was in charge of the reconstruction work. He chose to use lighter materials than those previously used, and changed the profile of the dome. Later, the damage caused by the earthquake of 869 was repaired by the Byzantine emperor Basil II and the Armenian architect Trdat. The church was reopened in May 994. In 1346, there was a collapse of some structural elements in the east side, which led to the closure of the building until 1354, when the repairs done by the architects Astras and Peralta were finished. (2) From the 15th–19th century. Shortly after the conquest of Constantinople in 1453, Mehmed II converted Hagia Sophia into the Ayasofya Mosque. He ordered the construction of the first minaret (the south-east one) and the plastering of the wall mosaics. Under the Sultanate of Selim and under the guidance of the Ottoman architect Mimar Sinan strengthening works were carried out, and two minarets and the mausoleum of the Sultan were built. One of the largest and most complete restoration works of Ayasofya was ordered by Sultan Abdul Mejid I, and completed between 1847 and 1849, under the direction of the architect Fossati. The dome was consolidated and the pillars 727 strengthened and straightened. Moreover, steel chains were inserted around the base of the dome, and the surviving Byzantine mosaics were discovered and covered with a new layer of plaster, while old chandeliers were replaced by new ones. In the upper columns, four circular medallions, painted by calligrapher Kazasker İzzed Effendi, were hung. On July 13, 1849, at the end of the restoration, the mosque was reopened for worship. In 1934, the building was transformed into a museum by Mustafa Kemal Atatürk (Necipoglu 1992). Since then, several studies have been conducted and there have been numerous restoration, reconstruction and consolidation works, many of which are still in progress. The monument today shows some structural deformations. These affect the arches, vaults, dome, and colonnades and show a state of instability that has accompanied it for a long time. The nave, which creates a space of about 30 m wide by 80 m long, is bordered by a series of piers and columns that separate it from the side corridors on the ground floor and the upper gallery. The nave, which ends with an apse in the eastern side, is covered by the dome, by two half-domes (Figure 1, letter G) and four exedras (Figure 1, letter F). The pendentives are located at the corners of the main dome (Figure 1), which has a maximum diameter of 31.24 m, and it is 55.6 m above the soil surface (Erdik and Croci 2010; Van Nice, 1965). The pendentives (Figure 1, point H) delimit the principal arches (Figure 1, letter B) and, together with the latter, they support the dome and distribute the weight of the dome to the pillars. Secondary arches Figure 1. Primary and secondary constructive system of the monument (from Mainstone, 2009). © Mainstone et al. Reproduced by permission of Mainstone et al. Permission to reuse must be obtained from the rightsholder. 728 M. CAPPA ET AL. are placed under the system of the principal arches (Figure 1, letter A). The walls under the upper arches in the northern and southern sides form the tympana. These walls are not visible from the interior, but only from the exterior of the monument. The materials used to build the dome, the pendentives, the half-domes, and the tympana are mainly bricks. In the Narratio de structura temple S. Sophiae the bricks used for the main arches and the dome came from Rhodes Island and they are 40–50 mm thick. The document also mentioned that the mortar is made of lime, sand, and brick fragments, and that the thickness of the mortar layers is 50–60 mm, wider than that of the bricks (Preger 1998). The base of the dome is made of marble blocks, while the dome itself is made of bricks. The reconstruction of the dome (Figure 2) carried out in the 6th century AD involved raising the dome 20 byzantine feet (approx 6.24 m). In the 10th century, a portion in the western side of the dome was reconstructed by the architect Trdat and, in the 14th century, a portion in the eastern side was rebuilt by the architects Astras and Peralta. Moreover, isolated interventions were carried out in the 10th century in the upper part of the northeast pendentive (Mainstone 2009). The pendentives are the triangular portions of the sphere that connects the quadrangular base of the dome with the hemisphere of the dome itself. Their history is related to that of the dome. The main interventions which have led to the current situation are those that interested the dome between the 6th and the 14th centuries. Figure 2. Map of the dome with the limits of the reconstructions (from Mainstone, 2009). © Mainstone et al. Reproduced by permission of Mainstone et al. Permission to reuse must be obtained from the rightsholder. The arches at Hagia Sophia are on two levels: the lower arches (Figure 1, letter A) supporting the tympana, and the upper arches (Figure 1, letter B) supporting the dome. The main interventions in which they were involved are: the reconstruction of the 6th century, after the collapse of the dome, of the eastern arch and the modifications of the south and north arches; ● the reconstruction of the western arch in the 10th century; and ● the collapse of the main arch in the 14th century and the following reconstruction. ● The upper and lower north and south arches have never been reconstructed and are symmetrical with different heights (Mainstone 2009). The tympana have suffered several reconstruction interventions due to the fragility of the colonnades that support them. They were completely re-built in the 6th and 10th century after the colonnades were destroyed. In the 14th century, the openings of the windows were reduced to try to give more stability to the walls. The main semi-domes have also been repaired following the events that characterized the history of the east and west portions of the building. The earthquake of the 6th century produced fractures in the east semi-dome. In the 10th and 14th century the main semi-domes were reconstructed at the same time as the dome. 3. Methodology The thermografic surveys were carried out with an IR thermocamera with an uncooled microbolometer detector, model SC640, produced by Flir Systems AB, with a 24° lent and electronic zoom 8x. The thermocamera has an IR resolution of 640 x 480, a thermic sensibility of 30 mK at 30°C with a frequency of image of 30 Hz. The view field is 24° x 18° (FOV) with a minimum focusing distance of 0.3 m. The maximum distance for a good acquisition of data depends on the differences of temperature between the object and the environment. At Hagia Sophia the maximum distance between the camera and the objects investigated has reached even more than 25 m. The accuracy of the instrument is maintained between ±1°C and ±1% in a temperature range reaching 120°C. The camera has a spectral field between 7.5 and 13 µm. The instrument also has an incorporated digital camera with a resolution of 3.2 megapixels, and it has an SD memory slot, in which thermal and digital images, as well as thermal videos are saved. INTERNATIONAL JOURNAL OF ARCHITECTURAL HERITAGE The software used to elaborate thermographic images is ThermaCAM Researcher Pro 2.10 and Tool+ produced by Flir Systems AB. The following protocol was applied for the thermographic research: ● ● ● ● ● preliminary identification of the points of the station; measurement of environmental conditions (parameters of room temperature, reflected temperature, relative humidity, and distances from the objects); insertion of environmental parameters and identification of emissivity parameter; identification of the areas to be inspected, acquisition of thermal images and the corresponding digital images; and post-processing data, analyses of thermograms and building thermal image mosaics. During the entire work, passive processes were used and, therefore, no heat sources were used in support of the thermographic surveys. The temperatures acquired were analyzed qualitatively evaluating the differences in temperature inside the individual thermal images. As previously stated, this work presents the results of the thermal study carried out on the main arches, the pendentives, and the tympana of the monument. 4. Results 4.1. Pendentives Following Mainstone (2009), all the pendentives were built using 40 mm thick bricks, interspaced with layers of lime mortar mixed with sand, with a greater thickness than that of the bricks (50–60 mm). The fact that the mortar is thicker than the bricks is probably due to the necessity of making a curvature in the pendentives that respected the geometric lines of the sphere. The thermographic inspections show the presence in the pendentives of materials that are different by type and size. Moreover, they allow us to identify some important differences among the four pendentives, thus testifying the presence of various construction phases and constructive methods used over the centuries. The thermographic investigation of the south-east pendentive (Figure 3) shows that the building materials are organized with regularity, following ordered lines of materials with different thermal characteristics. The material and typological continuity detected demonstrate a willingness to make the pendentives and the arches above the tympana more clamped, thus, more resistant to stress. 729 The choice of posing these horizontal and substantially equidistant lines of materials is associated with the fact that they are linked to the main southern arch. The thermal analysis shows that there are five lines in the pendentive (four of which correspond to those of the main arch in the south side). The thickness of these lines is almost the same. This type of masonry probably corresponds to the intervention of Astras and Peralta, which took place in the 14th century AD, after the earthquake of 1343 (Mainstone 2009). In the pendentive in the northeast side (Figure 4), located on the right of the apse, a geometric distortion is particularly evident already to the naked eye. This distortion testifies a junction between two non-contemporaneous parts. In fact, this point, which is visible to the naked eye at the top, shows the attempt to connect two parts that were built in different periods. The eastern area shows a portion of the masonry with the same lines detected in the south-east pendentive. In this area, the thermographic inspection shows the presence of a discontinuity in the materials used. The thermography shows a vertical strip of lighter color (Figure 4, point c) that testifies the point where the two masonries were joined together and there is an interruption of the horizontal lines of the east portion of the pendentive. In the north part, there is a different type of construction, characterized by the use of disordered and heterogeneous materials. Here it is not easy to recognize the restorations carried out in the 10th century reported by Mainstone (2009). Four lines can be clearly identified in the eastern portion. The lower ones are integrated at several points to the adjacent parts, but they tend to diverge from the original line. In this case, although the thickness of the lines of materials is similar to the previous pendentive, they are not equidistant, and there is no correspondence between the lines of the eastern part and the adjacent arch. Also in the northwest pendentive (Figure 5), it is possible to detect—through a thermographic inspection —lines of different materials. However, in this pendentive, differently from the previous one, there are only two lines. In the bordering part with the northern tympanum, there is a discontinuity in the upper line (Figure 5, point d). This discontinuity could indicate the boundary between the part that was re-built in the 6th century and the one that was built in the 10th century (Mainstone 2009). The thickness of these lines is less constant and smaller than the previous ones, probably because blocks of different size were used. The upper arch of the northern tympanum, bordering the pendentive, does not show any lines and, therefore, there is no correspondence between the lines of the pendentive and the upper arch. 730 M. CAPPA ET AL. Figure 3. Photo and thermal image of the south-east pendentive taken from the apse. Figure 4. Photo and thermal image of the north-east pendentive taken from the apse. Figure 5. Photo and thermal image of the north-west pendentive taken from the center of the nave. In the arch in the west side, although there are lines with different materials, they are not built with the same constructive order as the southeast pendentive, and the thickness of these lines is smaller than those in the adjacent pendentive. The other materials used show thermal homogeneity. The decorative surfaces of the south-west pendentive (Figure 6) have been recently restored. This pendentive is different from all the others. In particular, it is possible to differentiate three areas. The upper one (Figure 6 point e), at the edge of the south tympanum, does not show any lines and it is homogeneous in its material composition. Here, there are holes visible even to the naked eye. Thanks to the thermographic analysis, it is possible to understand that these holes only cross the wall of the pendentive, but do not cross the external wall. In fact, they appear of a dark color in the thermographic image (which means they are colder). If they had crossed the external wall they would have appeared of a lighter color (yellow/white), due to the higher temperature of the outside. INTERNATIONAL JOURNAL OF ARCHITECTURAL HERITAGE 731 Figure 6. Thermal image of the south-west pendentive taken from the center of the nave, which shows the three areas with important constructive differences. In the lower part of the pendentive (Figure 6, point f) the four almost equidistant thick lines are interrupted in the middle of the area. The part of the pendentive that is adjacent to the western arch (Figure 6, point g) is similar to the northwest pendentive. In fact, there are only two lines with irregular thicknesses, which is caused, also in this case, by the use of similar materials but with different thicknesses. Another singularity in this pendentive is the tendency of the line to be directed upward. In fact, the line is not parallel to the edge of the dome, but has an inclination towards the arch to the west. A similar situation can be observed, although to a lesser extent, in the northwest pendentive. The lines of the pendentives do not continue in the arches adjacent to the west and above the south tympana. 4.2. Main arches The arches located in the area corresponding to the apse and the main entrance (Figure 1, letter C) have undergone several reconstructions. From the thermal images this is evident because it is possible to observe that the arch to the west (Figure 9, point m) shows thin lines of different materials which are almost equidistant. However, these lines are not connected to those of the adjacent pendentives. In addition, these lines are thinner than the lines of the pendentives. In the central portion of the arch in the east side, it is possible to observe the presence of three lines. This could be interpreted as the result of an attempt to intensify the lines near the keystone of the arch. The arch in the east side, which delimits the central nave and the apse, was most recently rebuilt (Mainstone 2009). The thermographic inspection shows that this arch has the same characteristics as the arch in the west side. In the lower part of the arch, both in the north and south side, it is possible to observe the presence of blocks of material with different widths (Figure 3, points a and Figure 4, points b). Due to the fact that this material has similar thermal parameters in the northeast and southeast pendentives, it is possible to identify them as stone blocks. The northern and southern main arches (Figure 1, letter B) only partly belong to an older period than the other main arches. In fact, they were probably rebuilt in the 6th century (Figure 2) (Mainstone 2009). In the southern arch, the reconstructions that affected the portions bordering the pendentive in the eastern side are more evident. In Figure 8, in particular, it is possible to observe that the constructive technique of the eastern pendentive extends the lines to the arch. Instead, the central and western portions of the arch, do not show any lines, and they are composed of the same material up to the junction with the underlying pillar in the west side. Due to the thermal homogeneity, this latter portion, may be considered as the oldest one with no alteration and, therefore, attributable to the 6th century. The main arch in north side has no evident thermal dishomogeneity. Only in certain points on the border with the northwest pendentive, some sporadic lines can be observed (Figure 9, point n). However, they have a reduced thickness, compared to the lines of the southern main arch. The rest of the arch (Figure 4) shows the same construction material. Most part of the latter, due to its homogeneity, can be attributed to the earliest period of reconstruction of the monument (6th century). 4.3. Tympana and secondary arches The materials with which the tympana were made, are bricks (Mainstone 2009). The thermographic survey allows the collection of information on the building of the tympana. In the north side tympanum (Figure 7), it is possible to distinguish the height and the characteristics of the secondary arch. In fact, at the top, a wide strip with a 732 M. CAPPA ET AL. Figure 7. Photo and thermal image of the north tympanum taken from the dome. Figure 8. Mosaic of the thermal images of the south tympanum. thermographic images allow the observation of the border between the windows and the tympana masonry under the plaster. The material added to realize the narrowing has lower temperature values than the surrounding materials. This is why they can be attributed to the use of a different material from the rest of the wall. Comparing the results of the thermography and the historical sources cited by Mainstone (2009), it is possible to assume that this filling was the result of the intervention directed by the architect Sinan. The analysis of the south Tympanum (Figure 8) shows similar evidence. In fact, both the bounding arch (Figure 8, points h and i) and the narrowing of the windows can be observed (Figure 8, point l). However, due to the different exposure of the wall, compared to the previous one, the quality of the thermal image, does not allow us to “see” the parts made of different materials with the same clarity. The same narrowings are visible in the windows that can be observed on the right of Figure 8 and in the secondary arch, on the left of the image. 5. Concluding remarks Figure 9. Mosaic of the thermal images of the main arc, tympanum, pendetives and dome from the nave. different temperature, is visible. Furthermore, it is also possible to identify the presence of an intervention aimed to narrowing the windows. As a matter of fact, the The thermographic study has allowed the identification of differences in the materials and construction methods that have marked the historical evolution of the monument. It allowed us to distinguish the areas that suffered reconstructions, and within them, the use of different materials. It has also contributed to the resolution of the issues related to the understanding of the exact limits of the reconstructions carried out during the centuries. In particular, the pendentives show differences that can be attributed to different periods of reconstruction. The distinction between the various construction typologies and materials used has allowed the identification of the boundaries between the different reconstructions. This analysis, together with the data reported in INTERNATIONAL JOURNAL OF ARCHITECTURAL HERITAGE literature (Mainstone 2009) suggest that the portions built in the 6th century show only bricks, while in the pendentives that were rebuilt after the 6th century, blocks of stone were added to the bricks. The parts rebuilt in the 10th century, on the other hand, show two thinner lines made of stone. The experience of the previous collapses, probably led the 14th century workers to build some parts of the monument augmenting the number of lines (which, here, are 5, instead of 4) placing them equidistantly, with a greater “constructive knowledge”. As for the main arches, thermography has allowed us to note that the ones in the northern and southern sides show many differences, which are closely related to the restoration works performed on the pendentives over the centuries. Only few of the portions of the arches show no lines and are, therefore, homogeneous, whereas the arches in the east and west side, show an occasional use of different materials. The thermographic inspections on the tympana and on the secondary arches have determined the width of the arch, which has the same depth of the masonry. They have also highlighted an intervention of narrowing of the windows, made using different materials from the one used in the corresponding masonry. Finally, this research has demonstrated the validity of the thermographic survey for the study of monuments. This technique has been able to provide additional information on the limits between the different construction phases, thus proving to be a valuable tool for testing the hypotheses proposed by literature without any kind of intervention on the monument. The technological evolution of the instruments provided, has allowed us to obtain a high sensibility of thermography and, therefore, achieve results even at a great distance, in non-ideal climatic conditions and without the use of artificial heat. Acknowledgment We thank all the staff and the direction of the Hagia Sophia Museum for their helpfulness and hospitality and the Ministry of Culture of Turkey for the granting of all permits necessary for the conduct of investigations inside the monument. The work is part of the joint research activity of the Department of Biology, Ecology and Earth Sciences (DiBest) of the University of Calabria and the Archaeological Prospection Laboratory of the Antropoligicas Institute of Research, National Autonomous University of Mexico (UNAM). It also part of the research for the Ph.D. thesis of Murat Cura titled “Costruzione di un database multimediale per un approccio multidisciplinare alla diagnostica di Santa Sofia”, which is being carried out at the Scuola di Dottorato “Archimede” in “Scienze, Tecnologie e Comunicazione” 733 (XVII Ciclo), in the frame work of the DiBEST – “Dipartimento di Biologia, Ecologia e Scienze della Terra”, University of Calabria (tutor: prof. Gino Mirocle Crisci, prof. Luis Barba, and dr. Domenico Miriello). All the thermal images were acquired by Marco Cappa (Level 2 Thermographer ISO 9712). Funding The research was conducted with the contribution of the Department of Biology, Ecology, Earth of the University of Calabria (Italy), which funded the entire campaign survey, and of Flir Systems Italy who provided the equipment for the thermographic investigations. ORCID Alessandra Pecci http://orcid.org/0000-0001-9649-1112 References Avdelidis, N. P., and A. Moropoulou. 2004. 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