Alexandria was the ancient Egyptian city severely damaged by the tsunami that followed the 365 AD Crete earthquake.
The earthquake struck near Crete on July 21, 365, probably at about sunrise. Modern geological estimates place its magnitude at 8.5 or higher, making it one of the strongest known historical earthquakes in the Mediterranean. The resulting tsunami spread across much of the eastern and southern Mediterranean.
Alexandria and the Nile Delta were especially vulnerable because the city stood on a low, coastal landscape with busy harbours and densely settled waterfronts. The Roman historian Ammianus Marcellinus described the sea first retreating and then surging inland, carrying ships far from the shore. Alexandria reportedly commemorated the disaster for centuries as a “day of horror.”
The tsunami also devastated parts of Libya, Crete, Cyprus, Sicily and other Mediterranean shores. Thebes and Memphis were important Egyptian cities, but neither is the standard answer to this question: the historical descriptions specifically connect the catastrophic coastal damage with Alexandria.