The Diolkos (Δίολκος, from the Greek διά, dia "across" and ὁλκός, holkos "portage machine") was a paved trackway near Corinth in Ancient Greece which enabled boats to be moved overland across the Isthmus of Corinth. The shortcut allowed ancient vessels to avoid the long and dangerous circumnavigation of the Peloponnese peninsula. The phrase "as fast as a Corinthian", penned by the comic playwright Aristophanes, indicates that the trackway was common knowledge and had acquired a reputation for swiftness.

The main function of the Diolkos was the transfer of goods, although in times of war it also became a preferred means of speeding up naval campaigns. The 6 km (3.7 mi) to 8.5 km (5.3 mi) long roadway was a rudimentary form of railway, and operated from c. 600 BCE until the middle of the 1st century CE. The scale on which the Diolkos combined the two principles of the railway and the overland transport of ships remained unique in antiquity.

Function

The Diolkos saved ships sailing from the Ionian Sea to the Aegean Sea a dangerous sea journey round the Peloponnese, whose three headlands had a reputation for gales, especially Cape Matapan and Cape Malea. By contrast, both the Gulf of Corinth and the Saronic Gulf were relatively sheltered waters. In addition, the overland passage of the Isthmus, a neck of land 6.4 km (4.0 mi) wide at its narrowest, offered a much shorter route to Athens for ships sailing to and from the Ionian coast of Greece.