Legendary sunken island in the Atlantic Ocean west of Gibraltar. The main sources for the legend are two of Plato's dialogues, Timaeus and Critias. According to Plato, Atlantis had a rich civilization, and its princes made many conquests in the Mediterranean before earthquakes destroyed the island and it was swallowed up by the sea. Plato also supplied a history of its ideal commonwealth, and Atlantis is sometimes imagined as a utopia. The legend may have originated with the eruption c. 1500 BC of a volcano on Thíra, which was so powerful that it gave rise to earthquakes and tidal waves.