PLATO'S TIMAEUS (TIMAIOS)
Without Plato there would be no Atlantis. If the dialogues Timaeus (Timaios) and then the Critias (Kritias) hadn’t been written, or if, like so much ancient Greek literature, they had been lost, nobody would ever talk about Atlantis or go looking for it: no other ancient author of any kind ever mentioned the story until Plato did, even though a number (Herodotus, Thucydides, etc.) of them might have had good reason to do so, had the story been well known. So since the existence of Atlantis story depends on Plato, and Plato alone, any exploration of the island must start from his texts. This link takes you to a translation of the Timaeus (Timaios in Greek), where Atlantis emerges for the first time.
There is a more up-to-date translation, with commentary, in the course text book: Kershaw, S.P., A Brief History of Atlantis: Plato's Ideal State, London: Robinson, 2016