Ancient engineering of fish capture and storage in
southwest Florida
Victor D. Thompsona,b,1, William H. Marquardtc, Michael Savaresed, Karen J. Walkerc, Lee A. Newsome,
Isabelle Lulewicza, Nathan R. Lawresf, Amanda D. Roberts Thompsonb, Allan R. Bacong, and Christoph A. Walserh
a
Department of Anthropology, University of Georgia, Athens, GA 30602; bLaboratory of Archaeology, University of Georgia, Athens, GA 30602; cFlorida
Museum of Natural History, University of Florida, Gainesville, FL 32611; dDepartment of Marine and Earth Sciences, Florida Gulf Coast University, Fort Myers,
FL 33965; eSchool of Humanities and Sciences, Flagler College, St. Augustine, FL 32084; fDepartment of Anthropology, University of West Georgia,
Carrolton, GA 30118; gDepartment of Soil and Water Science, University of Florida, Gainesville, FL 32611; and hDepartment of Biology, The College of Idaho,
Caldwell, ID 83605
In the 16th century, the Calusa, a fisher-gatherer-hunter society, were
the most politically complex polity in Florida, and the archaeological
site of Mound Key was their capital. Based on historic documents, the
ruling elite at Mound Key controlled surplus production and distribution. The question remains exactly how such surplus pooling
occurred and when such traditions were elaborated on and reflected
in the built environment. Our work focuses on the “watercourts” and
associated areas at Mound Key. These subrectangular constructions
of shell and other sediments around centralized inundated areas have
been variously interpreted. Here, we detail when these enclosures
were constructed and their engineering and function. We argue that
these structures were for large surplus capture and storage of aquatic
resources that were controlled and managed by corporate groups.
archaeology
| Calusa | Florida | fisher-gatherer-hunters
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T
he study of hydrological engineering in the ancient world has
long fascinated archaeologists, many of whom saw such architectural feats as integral to the development of the state and
linked primarily to agricultural production. Less frequently
discussed is the role that such engineering played in the development of nonagricultural societies, specifically those that relied
upon aquatic resources. Indeed, such resources are thought to
have been the foundations of cultural complexity elsewhere in the
world (1–4). While most researchers are familiar with capture
technologies, we are only now beginning to understand these
engineered structures as they relate to storage and management
(5–8). This research takes important steps in enhancing our understanding of fishing societies that engage in complex engineering and the social and ecological relationships that they engender.
The focus of our research in Florida centers on how the Calusa
(9–11), a fisher-gatherer-hunter society, created, maintained,
and distributed surpluses of aquatic and wetland resources. Our
main research question is how such groups stored fish in the
absence of refrigeration in the warm, subtropical environment of
southwest Florida. Some of the more intriguing architectural
features in this region include “watercourts” found at several
large shell midden/mound sites (12). We define these watercourts as subrectangular constructions of shell and other sediments around centralized inundated areas. The earliest interpretation
of these features was that they were for fish storage (13); however, no research has systematically evaluated their timing of
construction and function. Many, however, have speculated
widely on their function without conducting the excavations
necessary to evaluate these ideas. For example, Schober (14)
argues that the Calusa managed conch ponds, presumably in
water courts. We find this interpretation untenable for a number
of reasons that we outline in a recent work (15), with the main
reason being that juvenile marine gastropods prefer shallow,
seagrass-rich environments that would have been difficult to
duplicate in watercourts. Thus, while many have speculated over
the years, the work presented here represents a systematic
www.pnas.org/cgi/doi/10.1073/pnas.1921708117
evaluation of these features that allows for an interpretation of
their function. Our work at the site of Mound Key (8LL2) reveals
the complex engineering behind these structures, as well as details of their chronology and function (Fig. 1). We suggest that
these structures functioned as large-scale fish traps and storage
facilities for live fish surpluses.
During the 16th century, Mound Key was the capital of the
Calusa kingdom, which stretched from the Florida Keys to just
south of Tampa Bay (16, 17). Mound Key is located in Estero
Bay, FL, and is an anthropogenic island comprised mostly of
midden shell and other sediments (18); in the 17th century,
Mound Key had a population of ca. 1,000 (19). The site covers
ca. 51 ha and is a complex arrangement of midden-mounds,
canals, watercourts, and other features. By AD 1000, the inhabitants had engaged in substantial modification to the island,
with the two largest mounds (mounds 1 and 2) reaching elevations of around 10 m and 6 m, respectively. Our research on
mound 1 documents at least three phases of construction and
repair for a large building(s) beginning around AD 1000. The
last iteration of the mound 1 structure is what we interpret as the
“house” of Caalus, the mid-16th century Calusa king. According
to Spanish documents, it was able to hold 2,000 people, and it is
where Pedro Menéndez de Avilés, the first governor of La
Florida, met the king and discussed terms (19, 20). Our finding of
these structures indicates that mound 1 was the likely seat of
power for a long-lived corporate group for around 500 y (20).
Significance
Fish were captured and stored by Native Americans of southwestern Florida in complex walled structures called watercourts,
constructed of shell and other sediments. These structures were
engineered with knowledge of tidal systems, hydrology, and the
biology of species to be stored in these courts. This work documents the considerable ability of the Calusa, a nonagricultural
society, to engineer systems that significantly alter their natural
environment. These structures are associated with an evergrowing population and complex system of governance among
the Calusa of Florida.
Author contributions: V.D.T., W.H.M., M.S., and K.J.W. designed research; V.D.T., W.H.M.,
M.S., K.J.W., L.A.N., I.L., N.R.L., A.D.R.T., A.R.B., and C.A.W. performed research; V.D.T.,
W.H.M., M.S., K.J.W., L.A.N., I.L., N.R.L., A.D.R.T., A.R.B., and C.A.W. analyzed data; and
V.D.T., W.H.M., M.S., K.J.W., I.L., N.R.L., and A.R.B. wrote the paper.
The authors declare no competing interest.
This article is a PNAS Direct Submission. C.B.R. is a guest editor invited by the Editorial
Board.
Published under the PNAS license.
1
To whom correspondence may be addressed. Email: vdthom@uga.edu.
This article contains supporting information online at https://www.pnas.org/lookup/suppl/
doi:10.1073/pnas.1921708117/-/DCSupplemental.
PNAS Latest Articles | 1 of 8
ANTHROPOLOGY
Edited by Christopher B. Rodning, Tulane University, New Orleans, LA, and accepted by Editorial Board Member Elsa M. Redmond February 24, 2020 (received
for review December 19, 2019)
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Fig. 1.
LiDAR digital elevation model of Mound Key showing the site’s prominent features.
The available evidence indicates that the Calusa had a large
population (ca. 20,000) and were one of the most politically
complex groups of hunter-gatherers of the ancient world. Thus,
we are left with one central question: How did the Calusa at
Mound Key provide and sustain food sufficient for the complex
political and social life observed in the 16th century? We argue
that part of the answer to this is that the Calusa engineered
sophisticated landscapes for the capture and storage of live
surpluses of fish, which could have been obtained on a regular
basis in the inshore estuarine bays.
While Mound Key’s layout changed over time, it is clear that
the canals, watercourts, and other features were thoughtfully
engineered. Given its location in Estero Bay, its engineers had to
consider the effects of the low-amplitude (<1 m) mixed tidal
pattern of the Florida Gulf Coast. Bisecting Mound Key’s two
main midden-mound complexes is a central Grand Canal running approximately southwest to northeast, measuring around
365 m long and averaging 28 m wide. At its northern terminus,
the canal (today a wetland) opens up to constructed causeways of
shell ridges and burial mounds. Several tributary canals break off
the main canal at right angles and lead to other areas of the site.
Two watercourts flank the southernmost section of the canal and
mirror one another in form (Fig. 1).
Our research questions at Mound Key are directly related to
the role that surplus production played in Calusa society. Specifically, how were surpluses acquired, processed, and stored, and
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how did they relate to the timing of construction of large-scale
storage facilities? To address these questions, we conducted
remote sensing and archaeological excavations at one of Mound
Key’s watercourts in 2017 (Fig. 2).
Remote Sensing
Light detection and ranging (LiDAR) data on the watercourts
indicate that the East Court and the West Court enclose a total
of around 6,000 square meters of mangrove wetlands. The East
Court measures ca. 42 m in maximum width and ca. 70 m long
along its longest axis. The West Court measures ca. 50 m wide at
its widest and ca. 75 m along its longest axis. The East Court is
slightly smaller than the West Court, ca. 2,670 and ca. 3,350
square meters, respectively. The average berm height of both is
ca. 1 m.
Each court has an opening in the berm on the northernmost
section facing the Grand Canal measuring ca. 10 to 12 m wide. It
is these breaks that we believe were once the locations of gates
made of perishable materials (e.g., wood, fiber), similar to those
that Cushing (13) observed. Interestingly, the southern canal’s
entrance point is directly in line with a pass between two mangrove islands and then further on to Big Carlos Pass, which leads
into the Gulf of Mexico (SI Appendix, Fig. S1). These openings
and orientation would have facilitated the transport of resources
from both the bay and the Gulf.
Thompson et al.
Coring
Prior to our larger excavations, we collected a series of hand
vibracores and small-diameter percussion cores in the area of the
watercourts (Fig. 2). These included one small percussion core
(MK2014-core 3) in one of the berms, four vibracores in the
West Court (1605-10, 1605-11, 1605-13, 1605-14), and one
vibracore (1705-25) in the canal connected to the courts (SI
Appendix, Figs. S5–S9). Core 1605-13 was located in the center of
the West Court, 1605-14 was 12 m to the southeast along the
court’s long axis, and 1605-11 was 10 m to the northeast along
the short axis (Fig. 3).
Core 1705-25 (see SI Appendix, Fig. S9) was extracted from the
Grand Canal. This core represents 202 cm (decompacted
thicknesses reported throughout) of deposition and has four
distinct facies (i.e., stratigraphic layers). From bottom to top,
Excavations
We conducted excavations along the northeast edge of the West
Court (excavations N-1 and N-2), on top of the ridge above
(excavation N-3), across and into a portion of the eastern berm
that defines the court itself (operation O), and along one of the
berms that delineates the East Court (operation P; Fig. 2).
The operation O excavations (O-1, O-2, O-3) began in
the middle of the West Court’s eastern berm and continued
northwest into its interior. The upper levels are comprised of
more nonshell sediments (e.g., fine sands and vertebrate remains) and fragmentary, mostly oyster, shell than the lower
portions, which grade into nearly whole shell below the water
table. The orientation of the shell fragments appears to be a
result of dumping for construction in both the upper layers. The
orientation of the shell fragments that grade into the first few
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Fig. 2. Location of cores and excavation units in the area of the West Court,
East Court, and Grand Canal.
Thompson et al.
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ANTHROPOLOGY
Both the West Court and East Court are also directly adjacent to smaller watercourts and appear in some cases to be
connected. In addition, there are two smaller possible “gates”
for each court measuring 7 m that lead to the exterior of the site
into the bay on each court’s southern end. Our analysis of topographic slope based upon LiDAR data reveals two graded
causeways leading up to mound 1 and mound 2 from their respective watercourts, connecting each court, possibly for moving food from them to the tops of the mounds (SI Appendix,
Fig. S2).
We conducted a ground penetrating radar (GPR) survey of
several areas. While the survey was limited due to the vegetation
and the proximity of the water table, which precluded large-scale
coverage near and in the watercourts, we did conduct survey line
profiles along the shoreline adjacent to the West Court (SI Appendix, Fig. S3). Our GPR radar profile of this area shows distinct changes in strata, one of which, as we discuss later,
corresponds to stratigraphic layers that appear to be the result of
large-scale burning events (SI Appendix, Fig. S4). The GPR data
indicate that this stratum, which appears as a high-amplitude
planar reflection, is not localized to just the two areas where
two excavations are located (see operation N descriptions later),
but rather extends along the shoreline of the watercourt for at
least 15 m.
their descriptions and interpretations are (i) olive gray, molluskrich muddy sand, representing a subtidal estuarine environment;
(ii) very dark grayish brown muddy sand with shell gravel,
interpreted as a Calusa activity surface; (iii) muddy sand
with coarse shell gravel, interpreted as a midden prior to the
canal’s existence; and (iv) black mangrove peat, representing the
infilling of the central canal. It is probable that the surface between the precanal midden and the canal fill represents an
erosional surface for maintenance of the canal. Likely, the canal
would have required some degree of upkeep in the form of
dredging to maintain an appropriate water depth for vessels to
pass through it. No evidence of disconformity exists elsewhere in
the core’s stratigraphy, indicating time is relatively conformable
for historic interpretation. The existence of estuarine sediments
at the core’s base and 2 m below NAVD88 (heights relative to
this datum shown in Fig. 3) indicates that the entire history of
Mound Key is represented with evidence of human occupation at
just above this depth.
The other four vibracores (1605-10, 1605-11, 1605-13, and
1605-14) were extracted from the West Court. The stratigraphy
of all four cores is comparable, with the upper three facies described and interpreted as (from lowest to highest) (i) sandy shell
gravel to muddy sand, representing a shell midden prior to the
existence of the watercourt; (ii) dark gray, organic-rich sandy
mud, representing the watercourt environment; and (iii) black
mangrove peat, representing the infilling of the watercourt by
mangrove root mass after the watercourt became inactive. Core
1605-13 is significantly longer than the other watercourt cores.
Its lowermost stratigraphy includes a light gray sand with shell
gravel, overlain by a dark brown-gray, organic-rich sandy mud,
interpreted as a Calusa activity surface. The base of this core sits
1.7 m below NAVD88, higher than the pre-Mound Key height
(of 2 m) in core 1705-25, suggesting that no pre-Mound Key
history was captured in any of the watercourt cores.
The sedimentology, stratigraphy, and paleoecology of the
watercourt facies are consistent with this environmental interpretation. The sediments are dark gray and organic-rich,
suggesting dysaerobic conditions within the substrate, something
indicative of poor or limited estuarine water circulation. The
grain size distribution is dominated by mud, and these muds
exhibit sedimentary laminations. Such characteristics are unlikely
in an open subtidal estuary. Here, the environment was dominated by suspension-load deposition, with little water agitation
and little to no infaunal activity that would otherwise disrupt the
laminations.
Our final core is a percussion core and comes from the West
Court berm. Designated as 2014MK-core 13, this core was
placed to look at the overall depositional processes of Mound
Key (18). The upper layer of this core represents the construction of the berm with sediments from the watercourt. We selected two samples from this core to help date the construction
of the courts.
Fig. 3. Fence diagram of cores from the West Court and Grand Canal showing examples of stratigraphic relationships and modeled radiocarbon date ranges
(68% probability). Stratigraphic columns are hung from NAVD88 (noted by the position of the red line). Similar lithofacies (activity surface, prewatercourt midden,
watercourt, black mangrove watercourt fill, etc.) are color-coded and correlated between neighboring cores. Sections have been decompacted; heights of section
tops and bottoms are shown in centimeters above or below NAVD88 and noted at the top right and bottom right, respectively, of each column.
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submerged layers indicates that the berm’s construction extends
below the current water level.
The eastern half of O-2 was our deepest excavation, which was
excavated well below the water table (SI Appendix, Fig. S10).
Under the constructed berm. there is a large expansive shell
midden comprised of many intact shells. This was apparent in
our excavations, as well as in our cores. This shell midden graded
into sediments characteristic of the current bay system in its
deepest levels. Below the water table, we encountered preserved
wood debitage and cordage, as well as Cucurbita sp. gourd/
squash seeds (SI Appendix, Fig. S11). This suggests that these
elements were possibly carpentry debris from dugout canoe
manufacture and/or the creation of racks for smoking/drying fish,
as well as parts of fishnets and potentially net floats.
Along the northeast edge of the West Court in excavations
N-1 and N-2, we encountered dark, distinct strata with many
fragments of carbonized wood suggestive of burning (SI Appendix, Fig. S4). In addition, there were many associated small post
molds. In comparison with post molds previously encountered in
excavations on the tops of the mounds, these posts are much
smaller and do not seem to represent structural support posts for
large structures, but rather appear to represent drying and
smoking racks (see ref. 20), similar to patterns observed in other
regions, such as in Peru (21).
The N-3 excavation was located on the ridgetop directly
northeast of the West Court. Interestingly, no post mold or other
features of discernable function were identified in this excavation. The upper strata of this excavation contain whole and
fragmented oyster with abundant vertebrate faunal remains and
artifacts. The lower strata, in contrast, contain more whole shell
and few artifacts.
Radiocarbon Dating
Establishing the chronology of construction for these watercourts
is important if we want to link their use to other Mound Key
architecture. To do this, we obtained 22 AMS dates from our
excavations and cores (SI Appendix, Tables S1–S3). Two models
were constructed. The first model (model 1) was a threesequence sequential model to examine the timing of construction of the West Court berm (operation O and core 13), use of
the adjacent West Court shore line (N-1), the linear ridge adjacent to the West Court (N-3), and the construction of the
Grand Canal (core 1705-25; SI Appendix, Fig. S12). The other
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model (model 2) was a three-phase overlapping model to examine the onset of watercourt conditions from the cores taken in
the currently wet area of the West Court (cores 1605-13, 160514, and 1605-11; SI Appendix, Fig. S13).
Model 1 returned statistically significant results and shows
good agreement between the 14C dates and the model assumptions (Amodel = 104; Aoverall = 101.3; Fig. 4). It appears that the
Grand Canal, based on core 1705-25, is the earliest in the sequence of features. Understanding when this feature was in place
is critical to interpreting the functioning of the watercourts, as
they are thought to comprise a single hydrological system. The
model estimates deposits and the onset of the anthropogenic
activity surface to cal. AD 885 to 1010 (68% probability) and end
date of cal. AD 1015 to 1095 (68% probability). Thus, it appears
the canal was constructed and was an established hydrologic
feature a few hundred years before the construction of the West
Court (as detailed later).
Our N excavations are located on the former shoreline of the
large western half of Mound Key. This area also makes up a
portion of the West Court. This area too appears to have been
used prior to the construction of the West Court. Modeling of
the three dates for N-1 estimates a start date of shoreline midden
formation at cal. AD 1025 to 1120 (68% probability) and an end
date range midden formation activity in this area at cal. AD 1115
to 1155 (68% probability).
Operation O was across the West Court, with excavation O-2
going through the constructed berm down into prewatercourt
midden. Our model examines the formation of the prewatercourt
midden and the formation of the berms to construct the West
Court. In this part of the model, there is a sequence of three
radiocarbon dates from the excavations and two dates modeled
as a phase from core 13 in a stratigraphic order. In addition, the
dates from N-3 on the ridge adjacent to the West Court overlapped considerably with the ones from operation O and core 13
and were therefore modeled as an overlapping phase with these
dates. The three dates from operation O that are part of the
prewatercourt midden are in stratigraphic order and agree with
the overall model. Only one of the two dates from the berm
agrees with the overall model, with the other showing poor
agreement (UGAMS 20071). This, however, is not surprising if
the berm was constructed from contemporary or slightly older
midden deposits, a pattern observed in other deposits (18). The
model places the start of the prewatercourt midden at cal. AD
Thompson et al.
ANTHROPOLOGY
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Fig. 4. Probability distributions for model 1 (Left) and model 2 (Right) from cores and excavations from the West Court and Grand Canal. The clear line and
black together represent calibrated distributions and the black lines represent the posterior density estimates based on the models.
1285 to 1305 (68% probability). The model places the end date
range of construction of the watercourt at cal. AD 1385 to 1405
(68% probability). These ranges mark the date from which the
accumulation began to the end date of watercourt construction,
not the end of its use. Therefore, at some point between the start
of the prewatercourt midden and end range of construction, the
West Court was built.
Model 2 is of the three vibracores in the West Court and
dovetails with the results of model 1. To further understand the
timing of the canal vis-à-vis the construction of the watercourts,
we selected three samples from each core for dating. The
stratigraphically lowest radiocarbon date comes from the end of
the subtidal estuary deposits and before the onset of the midden
deposition. The second lowest sample comes from right after the
onset of the precanal midden. The third and stratigraphically
highest radiocarbon date comes from right at the end of the
precanal midden, just before the onset the of the central canal
fill. The model shows a good overall agreement (Amodel = 128.2;
Aoverall = 112.4) and refines the radiocarbon dates for the initial
layers of the prewatercourt basal midden deposits in the West
Court (Fig. 4). In each core, the model estimates the start of
prewatercourt midden at 68% probability as cal. AD 915 to 1145
(core 1605-11), cal. AD 1070 to 1295 (1605-13), and cal. AD
1105 to 1315 (1605-14). The end boundary for each core brackets
the onset of use of the watercourt and is as follows: cal. AD 1070
to 1295 (core 1605-11), cal. AD 1285 to 1345 (core 1605-13), and
cal. AD 1315 to 1475 (core 1605-14).
Thompson et al.
Vertebrate Faunal Analysis
To evaluate patterns of fish capture, storage, consumption, and
disposal at Mound Key as they relate to the function of the
watercourts, the vertebrate faunal remains recovered with
¼-inch mesh screen from operations N and O were analyzed.
Overall, remains of fish (Actinopterygii and Chondrichthyes)
account for the majority of NISP (number of identified specimens) and MNI (minimum number of individuals) in these assemblages, and a variety of fish taxa typical of Estero Bay is
represented. The period-III/IV (AD 1200 to 1500) contexts,
contemporaneous with the West Court, show that no fish taxon,
including mullet (Mugil spp.), dominates the assemblages.
However, when compared to the earlier, period-IIB (AD 800 to
1200) fish assemblages (SI Appendix, Fig. S14), the III/IV samples indicate an increase in mullet percentages, measured by
NISP and MNI relative to total fish.
Museum collections of ¼-inch–screened vertebrate faunal
remains from multitemporal midden contexts at Pineland,
Mound Key (operation C), and a group of other sites in the
Charlotte Harbor/Pine Island region also were reexamined with
a focus on mullet (SI Appendix, Figs. S15–S17). The regional
samples were smaller in area but were fine-screened (<¼-inch
mesh). Again, results show that later samples contain more
mullet remains than those dating to earlier times. Like the
Mound Key N and O assemblages, this is true based on NISP,
MNI, and their relative percentages of total fish. Although none
of these samples—like N and O—show a dominance of mullet,
the fact that a pattern of increased mullet is repeated in all cases
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Fig. 5. Specimens of mullet (Mugil sp.) fish scales recovered from the West Court core 1605-14 (Figs 2 and 3), sample 72 to 77 cm, one of several representing
the watercourt facies. Image credit: Zachary S. Randall (Florida Museum of Natural History, Gainesville, FL).
supports the idea that there may have been an increased regional
focus on capturing mullet coeval with the watercourts. Within
this pattern, of note, one of the latest IV-period samples from
Mound Key’s operation C exhibits a significantly higher mullet
percentage (58% MNI) than all others, suggesting that Mound
Key, in particular, may have been a late center for mullet production. Operation C was located on a 3.09-m-high shell-midden
ridge just to the east of Mound 1. This ridge may have been the
disposal area for the remains of fish and shellfish that were taken
to the summit of mound 1 for consumption.
Another analysis focused on the small, fragile remains present
in several of the West Court’s coarse (¼-inch) and fine (<¼-inch)
screened vibracore samples representing the watercourt facies (SI
Appendix, Table S4). Specifically, fish bone and scale specimens
were identified in the watercourt facies of cores 1605-13 (17 NISP)
and 1605-14 (123 NISP). Their numbers can be considered
abundant compared to an open estuarine bay setting, where fish
remains are rarely if ever found in subtidal sediments. In our
parallel work to reconstruct the bay history, we conducted coring
away from the site (n = 5) itself. Employing the same screening
techniques, we found that fish remains are essentially absent from
bay sediments and through a few thousand years of estuarine
history. Two of these cores (1703-21 and 1703-22) were taken
from shallow, soft-bottom, subtidal environments just east and
west of Mound Key with the explicit purpose of comparing facies
here with those from the watercourt (SI Appendix, Figs. S18 and
S19). Again, there are no fish remains in these cores. The relative
abundance of scales from the watercourt, subtidal muds is highly
unusual and not likely given background taphonomic processes. In
the watercourt cores, many of the scale specimens (Fig. 5) are
ctenoid forms and compare well with modern scales of the region’s
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mullet (Mugil) species, Mugil cephalus, Mugil curema, and Mugil
trichodon, the three being archaeologically indistinguishable. A
few other specimens compare well with modern herring
(Clupeidae) and pinfish (Lagodon rhomboides) scales. Consistent
with these are three herring vertebrae and a [cf.] pinfish quadrate. Herring and pinfish remains are typically abundant in <¼inch mesh-screened midden samples from Pine Island Sound
sites just to the north. The presence of scales and small specimens of these three schooling fishes (i.e., netable/trappable) in
the watercourt facies makes sense if the enclosures were used for
holding fish temporarily while consumption and disposal occurred on or near the mound summits.
Hydrological Experiments
To test the hypothesis that Mound Key watercourts conserve
enough water to maintain live fish—and possibly shellfish—
populations between high tides, we constructed hydrologic
models from measurements of hydraulic conductivity (Ksat) of
the West Court berm sediments and architecture (SI Appendix,
Supplementary Material). Using Darcy’s Law (22), our models
temporally constrain water loss from the West Court under two
berm compaction, or bulk density (Db), scenarios that capture
the range of typical uncompacted (bulk density = 1.4 g cm−3) and
compacted (bulk density = 2.0 g cm−3) soils. Further, because
LiDAR data suggest the presence of a sill, our models also
constrain water loss rate under two sill height scenarios (0.30 and
0.45 m) for both berm compaction scenarios.
Our hydrological model results (Table 1) indicate that West
Court water level would lower to 0.2 m (an assumed minimum
height to sustain fish) at 20.7 h and 26.8 h after high tide and lower
to 0 m at 72.7 h and 78.8 h after high tide with uncompacted berm
Thompson et al.
Model
1
2
3
4
Description
Db, g cm−3/Ksat, μm s−1
Time to 0.2 m of water, h
Time to 0 m of water, h
Uncompacted with 0.30-m sill
Uncompacted with 0.45-m sill
Compacted with 0.30-m sill
Compacted with 0.45-m sill
1.4/123
1.4/123
2.0/9
2.0/9
20.7
26.8
275.2
355.7
72.7
78.8
965.1
1,045.5
sediments and a 0.30-m and 0.45-m sill, respectively. With compacted berm sediments, West Court water level would lower to
0.2 m at 275.2 h and 355.7 h after high tide and lower to 0 m at
965.1 h and 1,045.5 h after high tide with a 0.30-m and 0.45-m sill,
respectively. Considering that the tidal cycle of Estero Bay is
roughly 12 h (23), our temporal estimates not only distinguish these
architectural features as effective water-holding structures, they also
demonstrate that compaction and sill height appreciably influence
watercourt hydrology, factors that were likely considered by the
Calusa in construction. Although our hydrological estimates
are extremely conservative (see SI Appendix, Supplemental Materials), they still provide water retention estimates that can exceed, sometimes by more than an order of magnitude, the Estero
Bay tidal cycle and thus provide support for the hypothesis (SI
Appendix, Fig. S20 and Tables S5 and S6).
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Data Availability Statement
All physical archaeological materials (i.e., artifacts, sediment
samples, paperwork) are curated at the Florida Museum of
Natural History for future reference. Copies of all digital data
(i.e., excavation database, digital photographs, and drawings) are
curated at both the Florida Museum of Natural History and the
University of Georgia Laboratory of Archaeology. These data
are available upon request from these repositories. All data
relevant to the arguments presented in this study can be found in
the manuscript and SI Appendix.
Discussion and Interpretation
The first line of evidence that these structures are more than
accumulations of midden remains lies in their physical form. As
we note, both the West and East courts are roughly rectangular
and symmetrical, adding to the degree of bilateral symmetry of
the site. Each court, in similar locations, contains an opening, a
“gate,” allowing access to its interior (SI Appendix, Fig. S21).
This layout also could have facilitated the capture of fish. If,
during certain times, the Calusa strung nets across the southern
end of the canal nearest the courts and opened the gates, fish
could then be easily corralled into the watercourts.
A second line of evidence comes from the N-1 and N-2 excavations and GPR survey, which provide evidence of fish
processing in the form of small post features and layers associated with drying and smoking racks, along what was the shoreline
prior to watercourt construction. Dates for this shoreline use
correspond to the time when the two largest mounds reached
almost their zenith and the earliest construction of the “king’s
house” on mound 1 (18, 20). Excavation across and into the West
Court berm (operation O), combined with coring of the court’s
interior, demonstrate the reconfiguring of the shoreline into a
court form corresponding temporally with the second phase of
the king’s house (20). Furthermore, the presence of fish elements, primarily mullet scales, in the West Court sediments,
particularly when such remains are not typically found in the
bay’s open-water subtidal environments, supports the interpretation of fish storage in the courts (Fig. 5).
Through time, this area of Mound Key clearly was the focus of
fishing-related activity including procurement, processing, canoe
manufacture, and fishnet use (if not also construction and repair). The latter two may be evidenced by waterlogged wood and
netting remains from O-2. It appears that the watercourts were
Thompson et al.
constructed to intensify (i.e., store for later processing) the
production of mullet and possibly other fish and shellfish. The
regional pattern of increased mullet through time, most significantly noted near mound 1 (operation C) coeval with the West
Court, supports the idea that mass capture and short-term
storage of mullet may have provided a primary surplus food
for the Calusa. While we do not know the chronology for the two
graded paths leading up to the mound summits, they likely facilitated the movement of processed foods to the inhabitants of
these mounds. The N-3 excavation, at the top of the West Court
ridge leading to the graded way to mound 2’s summit, exhibited
some of the latest midden, which included numerous fish remains. The greatest quantities of mullet remains, however, were
located behind mound 1 (operation C), in other words, just offmound of the king’s house (SI Appendix, Fig. S22).
The creation of surpluses required overcoming considerable
challenges in terms of storage and distribution of products.
Mound Key is located in a subtropical climate, which surely
would have caused problems for maintaining the surplus stability
and freshness, particularly with animal products. We suggest that
the Calusa of Mound Key were able to solve this unique problem
in a highly sophisticated manner, which partly involved keeping
live fish in watercourt storage areas. The construction of these
facilities would have likely required coordinated effort and collective buy-in from larger segments of society (20).
Surplus food stores in particular are frequently used to support large-scale labor projects and feasts, as well as a host of
other institutions in human societies that lead to greater investments in complex social and political formations (24–28).
Based on our modeling of the radiocarbon dates from the
watercourt excavations and cores, it appears that the Calusa built
these structures between AD 1300 and 1400. This chronology
corresponds with the tail end of the second phase of the king’s
house on top of mound 1 at the site. Shortly after this time, the
Calusa initiated the final phase of construction on this large
structure, adding additional deposits to the mound and modifying the large house, the one that Pedro Menéndez de Avilés
would see during his visit in 1566 (19). We also know from 16thcentury Spanish documents that certain sections of Calusa society (i.e., warriors, royalty) did not have to produce their own
food. We argue that continued population growth and the increasingly centralized power of ruling lineages at Mound Key
were likely underwritten by the surplus production of fish, akin
to such trajectories observed among stratified agricultural
societies (29).
We argue, following our earlier work at the site (20), that the
creation of these large surplus storage areas was part of a collective fiscal strategy of powerful house lineages to support an
increasingly complex political structure. As Blanton and Fargher
(30) note, collective strategies for state-building are dependent
upon buy-in from the general populace to support such endeavors. Large-scale public storage in watercourts is an effective
means by which various segments of Calusa society could be
engaged in the functioning of the capital and polity in general.
The growth of the Calusa polity and the power and influence
of Mound Key would have been a highly complex system that
required a large degree of confidence (i.e., food security and
surpluses) among participating groups to build such a system. In
sum, we view the construction of the watercourts as part of the
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ANTHROPOLOGY
Table 1. Parameters and results for watercourt hydrologic models
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economic base of Mound Key’s prominence as the capital. The
Calusa were capable of creating anthropogenic islands and
constructing canals, commanding a military, and controlling vast
networks of trade throughout Florida, among many other characteristics usually associated with better-known polities of the
Americas (e.g., Cahokia, the Maya). Ultimately reaching their
zenith in the 16th century at the time Europeans began landing
on their shores, they are one of the few examples of this level of
political complexity not supported by large agricultural surpluses,
but rather by the bounty of the sea.
ACKNOWLEDGMENTS. We thank the Florida Museum of Natural History
(FLMNH) at the University of Florida, the Department of Anthropology at
the University of Georgia, the Center for Applied Isotope Studies at the
University of Georgia (UGA), the Environmental Pedology and Land Use
Laboratory at the University of Florida, and the Florida Bureau of Archaeological Research. Finally, we very much appreciate the help and support of
Ted, Todd, and Tim McGee for allowing us to work on their property at
Mound Key. A number of individuals from Florida Gulf Coast University’s
Conservation Paleobiology Laboratory, UGA, and the University of Florida
provided field and laboratory assistance, including Aidan Arruza, Samantha
Gibson, Erica Krueger, Jenna MacDonald, Rebecca May, Kylie Palmer, Jonathan Wittig, Matthew Colvin, Brandon Ritchison, Isabelle Lulewicz, Nate
Lawres, and Michiel Kappers. We also thank Tony Krus and two anonymous
reviewers for their comments on the manuscript. Funding: Research at
Mound Key was supported in part by a grant from the National Geographic
Society (W411-15), the John S. and James L. Knight Endowment for South
Florida Archaeology, and a collaborative research grant from the NSF
(no. 1550909). Any opinions, findings, conclusions, or recommendations
expressed in this material are those of the authors and do not necessarily
reflect the views of the NSF.
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