The Isthmus of Corinth is a narrow strip of land that connects Central Greece with the Peloponnese, while the canal that has been opened in it connects the Saronic Gulf with the Gulf of Corinth. It is about 6 kilometers long and the narrowest point is where the Corinth Canal was built (1880-1893). It was a strategic point and for this reason a wall had been built since ancient times (late 5th century BC), which had been preserved until the Byzantines (Examilion).
The isthmus of Corinth was known in the ancient world as the landmark that separated the Peloponnese from the rest of mainland Greece. In the 1st century AD. the geographer Strabo pointed out a column in the isthmus of Corinth, which bore two inscriptions. One to the East, ie the Megara of Attica, which said: "τάδ᾽ οὐχὶ Πελοπόννησος, ἀλλ᾽ Ἰωνία" and the other to the West, ie the Peloponnese: "τάδ᾽ ἐστὶ Πελοπόννησος, οὐκ Ἰωνία". Plutarch attributed the construction of this column to the hero of Attica Theseus on the way to Athens.
Since 1893, the Corinth Canal has been opened in the 6.3 km wide isthmus, which in practice makes the Peloponnese an island. Today, two road, two railway and two submersible bridges at both ends of the canal connect the mainland side of the isthmus with that of the Peloponnese. At the western end of the canal is also a military emergency bridge.
