The original and initial source for Atlantis is the work of the ancient Greek philosopher Plato. Two of his dialogues Timaeus and Critias, which were written around 360 BCE, feature conversations between various characters. One of the characters in these dialogues, Critias, tells of a tale that has come down to him fourth-hand, supposedly from an Egyptian priest from around 600 BCE who in turn was linking knowledge conserved for 9,000 years, which was recorded in inscriptions on columns in the city of Sais. This tale, which is used to illustrate the nobility of the ancient Athenians, describes Atlantis as a great civilization from the West that dominated the Western Mediterranean from its base ‘beyond the Pillars of Hercules’. Normally these pillars are taken to refer to the Straits of Gibraltar, which separate the Mediterranean from the Atlantic, placing the land of Atlantis in what we now call the Atlantic Ocean. Both the name of the lost continent and the name subsequently given to the ocean refer to Atlas, the first high king of Atlantis, equivalent to the Titan of myth who supported the world on his shoulders. (Although Plato gives his Atlas a different parentage to the Titan, it is generally assumed that the two are cognate.)
Plato depicts Atlantis in some facet. It was roughly oblong, about 700 kilometers (435 miles) across, with mountains around the coast and a great central plain, the most prominent feature of which was a mount to the south, upon which a great acropolis was built and around which grew the capital city of Atlantis. The central acropolis was protected by concentric rings of canals, with mighty walls shielding each ring of prevailing land. A huge canal linked the circular moats with the ocean to the south, and all the commerce of the world passed up and down the great waterway. At its height, Atlantis was a glorious Bronze Age civilization, with a mighty army and fleet, rich in natural resources and prosperous from the trade of nations.
Plato also describes how Atlantis was created: Poseidon, god of the sea, took it for his own when the gods of Olympus were carving up the world, and he shaped it according to his needs. His children (the eldest of whom was Atlas) became the kings of the land and ruled according to his precepts. In a familiar tale of decline, however, they became morally corrupt and debased as their wealth and power increased, and so the gods visited disaster upon them, smiting the land with a great earthquake that caused it to sink beneath the waves, becoming an impassable mud shoal that hindered free transport between the Mediterranean and the Atlantic. These questionably unsteady foundations have given rise to many libraries’ worth of assumption from ancient times until the modern day.