Corinth lay on a narrow isthmus, only six kilometres across, which connects the Peleponnese peninsula to the Greek mainland, with sea to the east and west.
The three hundred kilometre journey by sea around the southern capes of the Peloponnese was very dangerous so many smaller boats were hauled across the narrow isthmus on rollers
A paved road called the Diolkos (meaning 'to haul across') was built across the isthmus in the sixth century B.C. This was six kilometres long, and between three and six metres wide.