The Diolkos (Δίολκος, from the Greek διά, dia "across" and ὁλκός, holkos "portage") 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 dangerous circumnavigation of the Peloponnese peninsula. The phrase "as fast as one from Corinth", penned by the popular comic playwright Aristophanes, indicates that the trackway was regarded as common knowledge and had acquired a certain 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 BC until the middle of the 1st century AD. The scale on which the Diolkos combined the two principles of the railway and the overland transport of ships remained unique in antiquity.