This is fascinating! From the Web (with slight editing by me!): It was Periander who first considered to open a Canal through the Isthmos. Demetrios Poliorketes seriously considered the idea and started working on it, but he was warned that the difference in sea levels would drown Aigina and other small islands. Nero sent 6000 Jewish slaves who dug a ditch 3300 meters in length and 40 meters wide, but the project was abandoned. Herod of Atticos, the Byzantines, the Venetians, they all tried. The Canal was opened after the Greek independence and between the years 1882 - 1893.