Crossing the Isthmus, the Six-Mile wall stretches from the Saronic Gulf to the Corinthian Gulf. Built to protect against attack from the North, it is also known as the Justinian Wall. In its day, it was the largest protective wall in the Greek world, with a length of 7.5 km and a width of 3 m, with 67 watchtowers. It takes advantage of the lines of the natural landscape, and was built (for better or worse) of recycled materials from classical-era structures, such as the nearby temple of Isthmian Poseidon.
Archaeological site of Ancient Isthmia