The geology of the southern coast of the Gulf of Corinth shows that the history of the related basin can be divided into two phases. During the first phase, the basin (called here proto-Gulf of Corinth) was filled with continental and shallow-water deposits, and was probably open to the east. During the second phase, the Gulf of Corinth assumed its present configuration. Sediments related to this second phase were Gilbert-type deltas and deep-sea deposits. During this phase the basin was connected to the Ionian Sea through the Gulf of Patra. This implies that the Peloponnesos, responding to the opening of the Aegean Sea, opened to the east via a movement hinged south of Patra. During the second stage, the extension direction shifted to north-south and broke the Hellenic mountain chain. This second phase can be related to a second generation of faulting that gave the basin its present shape.