IsthmusBy Jimmy Joe·August 8, 1999The Isthmus of Corinth joined the Peloponessus to mainland Greece. The Isthmus also separated the Gulf of Corinth in the north, from Saronic Gulf in the south. Two major cities have mythological stories: CorinthMegara Related InformationNameIsthmus of Corinth, Isthmia.Corinthia, Κορινθία.