Atlantis is the subject of a legend about an advanced island civilization that was destroyed or lost. Stories about Atlantis are first mentioned in Plato's dialogues Timaeus and Critias, in which characters say it was destroyed by an earthquake or a tsunami about 9,000 years before the time in which Plato wrote. The story claims Atlantis was somewhere outside the Pillars of Hercules. According to Plato, the story originated with Ancient Egyptian priests.

Some people believe that the stories are fictions made up to serve the purposes of Plato's dialogs. But others take them as if they were serious historical accounts. There have been dozens — perhaps hundreds — of locations proposed for the classical 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 1950s, most "Lost Continent" theories of Atlantis have been proven conclusively false.

Some cultures have "lost civilization" myths. In some cases, it has been argued that there is a common historical event or real "lost civilization" at the root of some or all of these legends, but there is considerable disagreement between the competing hypotheses. It may be that these legends have arisen from many different historical events, and are only just now being associated by modern theorizers because of their similarity. It may also be that these legends are entirely fictional, but for some reason have arisen and remained popular in many different cultures at different times.