Atlantis was a legendary ancient island, whose existence and location have never been confirmed. The first mentions we have are from the classical Greek philosopher Plato, who said that it was destroyed by possibly an earthquake or a tsunami about 9,000 years before his own time. Plato claimed it was somewhere outside the Pillars of Hercules (also known as the Strait of Gibraltar).
According to historical accounts, the story of Atlantis was about the conflict between the ancient Athenians and the Atlanteans around 9,000 years before Plato's existence. The origins of the story of Atlantis date back to Egyptian priests who transfered it to Solon. Soon Solon passed the tale to Dropides, who was the great-grandfather of Critias. And Critias learned of it from his grandfather also named Critias, son of Dropides.
There have been dozens � perhaps hundreds � of locations proposed for Atlantis. Some are more-or-less serious attempts at legitimate scholarly or archaeological works; others have been made by psychic or other pseudoscientific means. As continental drift became better understood and accepted during the 1950's, most "Lost Continent" theories of Atlantis have been proven conclusively false.

http://en.wikipedia.org/wiki/Location_hypotheses_of_Atlantis

17 placemarks of differents hypothesis