Between March 1965 and September 1966, two strong earthquakes occurred in central Peloponnesus (Greece). The first shock was connected with the west wall of the Megalopolis depression and it was followed by another shock connected with the opposite wall. The cumulative effects of these two earthquakes, and of two other deeper shocks that occurred further north, were considerable and difficult to separate. Landslides and slumping of the ground accounted for the majority of the damage which increased progressively with the shocks that followed. Submarine and coastal slumping caused additional damage and a small sea-wave was set off in the Gulf of Corinth. At the epicentral area the ground movements were severe, with a double amplitude on the record-plate of a standard Wilmot seismoscope reaching 60 millimeters.