In the sixth year of the war a part of the Athenian works was destroyed by the sea, with half the ships on the beach destroyed. Thucydides reports that following an earthquake, the sea receded from the shore before returning in a huge wave.
During the sixth year of the war, part of Athens' fortifications were damaged by the sea, resulting in the destruction of half their fleet that was beached.  According to Thucydides, following an earthquake, the sea retreated from the shore before returning with a massive wave.