The Corinth Canal connects the Gulf of Corinth in the Ionian Sea with the Saronic Gulf in the Aegean Sea. It cuts through the narrow Isthmus of Corinth and separates the Peloponnese from the Greek mainland, arguably making the peninsula an island. The canal was dug through the isthmus at sea level and has no locks. It is 6.4 kilometres (4 mi) in length and only 21.4 metres (70 ft) wide at its base, making it impassable for many modern ships. It has little economic importance and is mainly a tourist attraction.
The canal was initially proposed in classical times and a failed effort was made to build it in the 1st century AD. Construction recommenced in 1881 but was hampered by geological and financial problems that bankrupted the original builders. It was completed in 1893, but, due to the canal's narrowness, navigational problems, and periodic closures to repair landslides from its steep walls, it failed to attract the level of traffic expected by its operators.
Several rulers of antiquity dreamed of digging a cutting through the isthmus. The first to propose such an undertaking was the tyrant Periander in the 7th century BC. The project was abandoned and Periander instead constructed a simpler and less costly overland portage road, named the Diolkos or stone carriageway, along which ships could be towed from one side of the isthmus to the other. Periander's change of heart is attributed variously to the great expense of the project, a lack of labour or a fear that a canal would have robbed Corinth of its dominant role as an entrepôt for goods. Remnants of the Diolkos still exist next to the modern canal.
The Diadoch Demetrius Poliorcetes (336–283 BC) planned to construct a canal as a means to improve his communication lines, but dropped the plan after his surveyors, miscalculating the levels of the adjacent seas, feared heavy floods.
The philosopher Apollonius of Tyana prophesied that anyone who proposed to dig a Corinthian canal would be met with illness. Three Roman rulers considered the idea but all suffered violent deaths; the historians Plutarch and Suetonius both wrote that the Roman dictator Julius Caesar considered digging a canal through the isthmus but was assassinated before he could begin the project. Caligula, the third Roman Emperor, commissioned a study in 40 AD from Egyptian experts who claimed incorrectly that the Corinthian Gulf was higher than the Saronic Gulf. As a result, they concluded, if a canal were dug the island of Aegina would be inundated. Caligula's interest in the idea got no further as he too was assassinated before making any progress. More details