According to Proclus, Crantor was the first to argue for the historicity of Atlantis. This is the beginning of what Proclus says about Crantor’s commentary on Plato:
“With respect to the whole of this narration about the Atlantics, some say, that it is a mere history, which was the opinion of Crantor, the first interpreter of Plato, who says, that Plato was derided by those of his time, as not being the inventor of the Republic, but transcribing what the Egyptians had written on this subject; and that he so far regards what is said by these deriders as to refer to the Egyptians this history about the Athenians and Atlantics, and to believe that the Athenians once lived conformably to this polity. Crantor adds, that this is testified by the prophets [i.e., priests] of the Egyptians, who assert that these particulars [which are narrated by Plato] are written on pillars which are still preserved.” (from Book 1, trans. Thomas Taylor, 1820)
Note, however, that Proclus does not say Crantor read these pillars, only that the Egyptian priests told him they exist. This is where most Atlantis believers leave off, with the alleged proof from the pillars of Egypt. But the text that immediately follows begins to make Crantor’s purpose clear. Bear with me. It’s long, and that is why it is rarely quoted:
From Proclus, Commentary on Timaeus
In short, Proclus’ statement of Crantor’s belief is less proof of the existence of Atlantis—or even belief in the existence of Atlantis—as much as it is proof that Crantor wanted to deny Plato’s critics the power to interpret the Timaeus and the Critias, to define Plato’s legacy, or to take from him the glory of his crowning achievement, The Republic.