Timaeus is one of Plato's dialogues, mostly in the form of a long monologue given by the title character, written circa 360 BC. The work puts forward speculation on the nature of the physical world and human beings. It is followed by the dialogue Critias. Speakers of the dialogue are Socrates, Timaeus of Locri, Hermocrates, and Critias. Some scholars believe that it is not the Critias of the Thirty Tyrants who is appearing in this dialogue, but his grandfather, who is also named Critias.
Critias is the second of a projected trilogy of dialogues, preceded by Timaeus and followed by Hermocrates, though the latter was possibly never written and Critias was left incomplete. Because of their resemblance (e.g. in terms of persons appearing), modern classicists occasionally combine both Timaeus and Critias as Timaeus-Critias.
In the dialogues Timaeus and Critias, Plato discusses political philosophy and makes the first mention of the Lost City of Atlantis, which he described in Timaeus as “an island which was larger than Libya and Asia together.” Plato continued, “Now in this island of Atlantis there existed a confederation of kings, of great and marvelous power, which held sway over all the island, and over many other islands also and parts of the continent.” Plato wrote that Atlantis disappeared under the sea in a single day.