Classical scholar Alan Cameron asserts ^{Cameron, Alan. Greek Mythography in the Roman World. Oxford University Press, 2004. p. 124}:

It is only in modern times that people have taken the Atlantis story seriously; no one did so in antiquity.

However, study of ancient commentaries reveal this statement to be demonstrably false. Some ancient writers did view Atlantis as fiction but others believed it was real.

The philosopher Crantor, a student of Xenocrates (who in turn had been a student of Plato), considered the story to be historical fact. His work, a commentary on Plato's Timaeus, is lost, but Proclus, a Christian historian of the fifth century AD, reports on it. The passage in question has been represented in the modern literature as both claiming that Crantor actually visited Egypt and had conversations with priests and saw hieroglyphs confirming the story, or as learning about them from other visitors to Egypt. Proclus wrote:

As for the whole of this account of the Atlanteans, some say that it is unadorned history, such as Crantor, the first commentator on Plato. Crantor also says that Plato's contemporaries used to criticize him jokingly for not being the inventor of his Republic but copying the institutions of the Egyptians. Plato took these critics seriously enough to assign to the Egyptians this story about the Athenians and Atlanteans, so as to make them say that the Athenians really once lived according to that system. The next sentence is often translated as Crantor adds, that this is testified by the prophets of the Egyptians, who assert that these particulars [which are narrated by Plato] are written on pillars which are still preserved. But in the original, the sentence starts not with the name Crantor but with the word 'He', and whether this referred to Crantor or Plato is the subject of considerable debate.

Proponents of both Atlantis as a myth and Atlantis as history have argued that the word should be translated as Crantor. Alan Cameron argues that it should be interpreted as 'Plato', and that when Proclus writes we must bear in mind concerning this whole feat of the Athenians, that it is neither a mere myth nor unadorned history:

Crantor's view as mere personal opinion, nothing more; in fact he first quotes and then dismisses it as representing one of the two unacceptable extremes.

Cameron also points out that whether 'he' refers to Plato or Crantor, it does not support statements such as Otto Muck's:

Crantor came to Sais and saw there in the temple of Neith the column, completely covered with hieroglyphs, on which the history of Atlantis was recorded. Scholars translated it for him, and he testified that their account fully agreed with Plato's account of Atlantis...

Or John V. Luce's suggestion that Crantor sent "a special enquiry to Egypt" and that he may simply be referring to Plato's own claims.

Or John V. Luce's suggestion that Crantor sent "a special enquiry to Egypt" and that he may simply be referring to Plato's own claims.

That an island of such nature and size once existed is evident from what is said by certain authors who investigated the things around the outer sea. For according to them, there were seven islands in that sea in their time, sacred to Persephone, and also three others of enormous size, one of which was sacred to Pluto, another to Ammon, and another one between them to Poseidon, the extent of which was a thousand stadia [200 km]; and the inhabitants of it—they add—preserved the remembrance from their ancestors of the immeasurably large island of Atlantis which had really existed there and which for many ages had reigned over all islands in the Atlantic sea and which itself had like-wise been sacred to Poseidon. Now these things Marcellus has written in his Aethiopica. Marcellus remains unidentified.

Other ancient historians and philosophers believing in the existence of Atlantis were Strabo and Posidonius. Zoticus, a Neoplatonist philosopher of the 3rd century AD, wrote an epic poem based on Plato's account of Atlantis.

Scholars dispute whether and how much Plato's story or account was inspired by older traditions. Some scholars argue Plato drew upon memories of past events such as the Thera eruption or the Trojan War, while others insist that he took inspiration from contemporary events like the destruction of Helike in 373 BC or the failed Athenian invasion of Sicily in 415–413 BC.

The possible existence of a genuine Atlantis was occasionally parodied by contemporaries. Writing only a few decades after the Timaeus and Critias, the historian Theopompus of Chios wrote of a land beyond the ocean known as Meropis. This description was included in Book 8 of his voluminous Philippica, which contains a dialogue between King Midas and Silenus, a companion of Dionysus. Silenus describes the Meropids, a race of men who grow to twice normal size, and inhabit two cities on the island of Meropis (Cos?): Eusebes "Pious-town") and Machimos "Fighting-town"). He also reports that an army of ten million soldiers crossed the ocean to conquer Hyperborea, but abandoned this proposal when they realized that the Hyperboreans were the luckiest people on earth. Heinz-Günther Nesselrath has argued that these and other details of Silenus' story are meant as imitation and exaggeration of the Atlantis story, for the purpose of exposing Plato's ideas to ridicule.

The 4th century AD historian Ammianus Marcellinus, relying on a lost work by Timagenes, a historian writing in the 1st century BC, writes that the Druids of Gaul said that part of the inhabitants of Gaul had migrated there from distant islands. Some have understood Ammianus's testimony as a claim that at the time of Atlantis's actual sinking into the sea, its inhabitants fled to western Europe; but Ammianus in fact says that “the Drasidae (Druids) recall that a part of the population is indigenous but others also migrated in from islands and lands beyond the Rhine" (Res Gestae 15.9), an indication that the immigrants came to Gaul from the north (Britain, the Netherlands or Germany), not from a theorized location in the Atlantic Ocean to the south-west. Instead, the Celts that dwelled along the ocean were reported to venerate twin gods (Dioscori) that appeared to them coming from that ocean.

While little known during the Middle Ages, the story of Atlantis was rediscovered by Humanists in the Early Modern period. Plato's description inspired the utopian works of several Renaissance writers, like Francis Bacon's "New Atlantis."

A Hebrew treatise ^{Selin, Helaine. Astronomy Across Cultures: The History of Non-Western Astronomy. Kluwer Academic Publishers, Netherlands, 2000. p. 574. ISBN 0-7923-6363-9} computational astronomy dated to AD 1378/79, apparently a paraphrase of an unknown earlier Islamic work, alludes to the Atlantis myth in a discussion concerning the determination of zero points for the calculation of longitude:

Some say that they [the inhabited regions] begin at the beginning of the western ocean [the Atlantic] and beyond. For in the earliest times [literally: the first days] there was an island in the middle of the ocean. There were scholars there, who isolated themselves in [the pursuit of] philosophy. In their day, that was the [beginning for measuring] the longitude[s] of the inhabited world. Today, it has become [covered by the?] sea, and it is ten degrees into the sea; and they reckon the beginning of longitude from the beginning of the western sea.