The Critias is one of Plato's late dialogues, an incomplete sequel to the Timaeus. The main speaker is possibly the historical Athenian aristocrat and relative of Plato, or his grandfather of the same name. Critias presents what is the earliest known version of the myth of Atlantis, a city which is said to have fought a war against prehistoric Athens. Plato's motive for presenting this story, which is attributed in the dialogue to an Egyptian source, has been debated ever since.
Free Online and Downloadable Texts
Gutenberg: The Critias, translated by Benjamin Jowett, multiple formats.
University of Adelaide (Internet Archive): Critias. EPUB, HTML and MOBI formats.
Wikisource: Critias, translated by Benjamin Jowett, online text.
Ancient Greece Declassified: Decoding Atlantis with Mark Adams, podcast by Lantern Jack.
Librivox: Critias - public domain audiobook.
PhilPapers: Plato - Critias - bibliography with open access option.
The Great Conversation: Further reading at Tom's Learning Notes
Ancient Greek resources: Learn to read Greek classics in the original.
Bloom's Western Canon: Plato's Dialogues are listed.