The city of Pavlopetri, in Vatika Bay underwater off the coast of southern Laconia in Peloponnese, Greece, is about 5,000 years old, making it the oldest submerged city known in the world. Pavlopetri is unique in having almost complete town plans, including streets, buildings, and tombs.
Originally, the ruins were dated to the Mycenaean period, 1600–1100 BCE but later studies showed a much earlier occupation dating back to 3500 BCE, so it also includes artifacts from the Final Neolithic Age, Chalcolithic Age, Bronze Age, and middle Minoan and transitional material. It is now believed that the town was submerged around 1000 BCE by the first of three earthquakes that the area suffered.
Discovered in 1967 by Nicholas Flemming and mapped in 1968 by a team of archaeologists from Cambridge, Pavlopetri is located between the islet of Pavlopetri and the Pounta coast of Laconia on the Peloponnese peninsula. The site is northeast of the village on the island of Elafonisos. The secrets of the lost city that may have inspired one of the world's most enduring myths – the fable of Atlantis – have been brought to light from beneath the waters of southern Greece.
According to the Wikipedia