It's told by Diogenes Laërtios, how Socrates was astonished by Plato's tales about him and said Plato was “writing so many lies (katapseudeth᾽) about me”. By this rather plausible account', Plato was not a faithful biographer. However even Socrates' philosophy was not about faithful biographies and Plato's writing might also be “false (pseudos)” in some aspect, but “true (alēthes)” in some other, i.e. a “merely” historical account in contrast to a philosophical discourse.
Even though Plato is known today for this “critique” of poets in his main work, Republic, this work is not a stand-alone, but rather a trilogy, since it's directly linked by internal references to other late dialogues, i.e. Timaeus and Critias. These works could give another perspective of Plato's understanding of himself as an artist — as which he was definitely considered by the later writers, e.g. Dionysios and Longinus who praise him as the master prosaist. We're now merely considering the last of this series, which is in a sense also the hardest one, since it's much more allusive than direct.
Critias is usually thought to be incomplete in a formal way — i.e. as if it was not in complete harmony with Plato's supposed goal of “finishing” this dialogue. This is not plausible even on merely philological grounds, since Plato is known to have been a careful writer, which is especially the case with Republic. It's rather more befitting to make a polished ending for the trilogy if the beginning is also that. It's not a commonplace enough to say, that Plato was an artist in the full sense of the word, keeping always an anxious eye on his long and short syllables, fretting himself about cases of nouns, moods of verbs, etc. like a careful clay-modeller.
The usual interpretation of Critias as “unfinished” is itself half-baked. One should at least suspect, that a man who is held to deserve greater reputation than any of his predeccesors, was very careful in composing his “eternal” works and submitting them to the scrutiny of all-testing envy and time — as they indeed have done. It's a basic principle of interpreting here, that no subject or word is merely random in Plato's dialogues, especially not in his most important and polished trilogy of the later years. Before composing Critias, Plato had stayed a long time in Egypt and familiarized himself with local ancient culture — much more so than the greek, who were, as the old saying goes, “mere babes” in comparison. It's not maybe suggested in vain, that Plato acquainted himself there even with the sacred scriptures of jews, i.e. Moses.
Considering the “historicity” of Atlantis, there's a whole tradition of passing the story of Atlantis merely from mouth to mouth, but the philosophical meaning is here completely lost in mere gaping at the mystery. Even so, Plato probably was inspired by some egyptian pillars, which according to later tradition actually existed, e.g. Crantor says he found them when visiting Egypt. An ancient egyptian story probably gave Plato food for thought, but it was never his meaning only to make a “historical” story in the sense a Herodotus or Thucydides were already writing in his time.
Plato the philosopher wrote many “lies” about even Socrates, even though he had much resemblance to the original — we can suppose this to be even more the case for the myth of Atlantis. However, even if it's not strictly “historical”, same should be said of the merely “mythical”. It's rather Plato's view that “history“ turns in to a kind of “myth“, i.e. an old wives tale, which is told only to make people gape in amazement, if it's not imbued with meaning. In this sense “historical” and “mythical” are equally opposed to philosophical.
What is the reason for Plato the philosopher to write a “historical” or “mythical” disguise for philosophy — and is this guise not rightful? Why not propound it merely head-on — head-on, like 'prorsus' in latin “prosa oratorio”, or “pezos dialektos” in greek — like Aristotle's lecture-course? Plato's Socrates mentions in the Republic an old greek proverb: “among the many (polloi) thyrsusbearers, only a few will become bacchi”. It's a basic attitude found among many religious communities, that the “hoi polloi” might misunderstand and ridicule their teachings for great harm, if they found out something about them, so it's better for them to know nothing.
This is a sort of safety “device“ many thinkers have since used and it has some resemblance to the so called socratic irony, i.e. something is said which is meant otherwise, which makes the discussion to have ambiguity and search for hidden meanings. Plato makes use of this stylistic “device” in many dialogues, if not in all of them, but if such a “device” is in harmony with the inner meaning, it's not an ornament made merely for playing, but quite earnest in it's ambiguity. Interpreting these kinds of artistic “devices” has some advantages, concerning how many philosophers have at least tried to use them, even if not properly. On the other hand, thinkers like Aristotle are so hard to follow, that even their mere lecture courses give an impression of loftiness, though many find it frigid.
Now, to give some illustrative examples, the profane are in greek 'bebēlos', like those-treaded-over, i.e. like they were on the treshold (bēlos) of a door leading to the interior temple — these tresholders, the ones on 'limen', to use latin equivalent, are left under the feet of those treading over, and as such the ones going over are the 'sub[-]limen', i.e. the sublime ones. Sentences like these might take some time to digest, even though they're quite straightforward. I'll for my part try and bite my way deeper into Plato's sacred walnut.
It's almost imperceptible how interpretation goes towards the definition of 'sublime', which is one of the most important ones when considering the philosophy of artwork — or rather the artwork of philosophy. There have been in history many different kinds of divisions for philosophy, e.g. logic is the shell, physics the egg-white, and ethics the egg-yolk. Philosophical divisions sound very much like baking and their history — like philosophy's relationship to artwork and religion — is easy as eating a cake.
In sublime there's always something more to be had — a feeling of not being finished. Certainly it's more befitting of living people to be considered like this, but with writing it's a bit more difficult. Many thinkers like to imitate the sublime style, even when their subject matter doesn't quite harmonize with it and then it eventually turns out frivolous. Such bombastic style is laughable, since it's like the mountains were working and a mouse came out. When deciding whether Plato's style in Critias is sublime or bombastic, one has to understand it's subject matter first — and there certainly are people whose understanding of the subject matter differs. This could make the style laughable, but interpreting it bombastic should presuppose a rather “full” understanding of the content.
To get back to the subject matter, the “dialogue”, or rather monologue Critias, tells the tale of an old city of Atlantis, which eventually sunk in deep mud, since they forgot the teachings of their predecessors. The philosophical point of the story is to eventually understand more deeply what happens to old tales in general — or rather, why and how philosophical discourses, which once have happened in live discourse, are transferred to writing and eventually sink in to the muddy sea of “hoi polloi”, who don't understand philosophy's about what. Even more, they won't merely keep on going, but dawdle along and smear all over philosophy “interpretations” — e.g. smudging platonic 'apofradas'.
The main story of Atlantis is on it's core about the war of gods, i.e. between Zeus and Poseidon, which is a sort of “gigantomachia peri ousias”. Atlantis is presented as the city of Poseidon, but towards the end of story Zeus starts the 'Theomachia' of Homer:
In the war of gods, everything is literally turned upside down: what comes first comes last, which was deep beneath comes the new upper, etc. The measure of god's war is heaven and earth and it's the greatest measure for the contemporaries of Homer — 'Theomachia' is rightfully a classical example of sublime. Another one, which goes well with this, is in the beginning of Moses' laws: “and God spoke thus (eipen ho Theos)”. Critias ends with the same lines, “theous […] eipen — ...” Zeus speaks and the war begins. The writings are “dead”, like the statues Xenophon mentions, i.e. they have no more a “voice to be heard” and this is also the problem Critias tackles with. The characters participating in Plato's trilogy are equally important, e.g. the third talker Hermokrates is a clear aptronym. Even as a historical figure he is “descended on his father's side from” Hermes, i.e. the god of interpretation, as one later historian points out.Then terribly thundered the father of gods and men from on high; and from beneath did Poseidon cause the vast earth to quake, and the steep crests of the mountains. All the roots of many-fountained Ida were shaken, and all her peaks, and the city of the Trojans, and the ships of the Achaeans. And seized with fear in the world below was Aidoneus, lord of the shades, and in fear leapt he from his throne and cried aloud, lest above him the earth be cloven by Poseidon, the Shaker of Earth, and his abode be made plain to view for mortals and immortals — the dread and dank abode, wherefor the very gods have loathing: so great was the din that arose when the gods clashed in strife.
According to philosophical standards Critias should be the first writing of Plato to read. It is indeed “unfinished”, but not according to it's form, since it's substance is being unfinished interpreting Plato's dialogues. Even if the substance of Plato's philosophy could be discussed without old age's love of telling stories — the flowing 'dramatikos' of his youth certainly suggests so, in contrast to his setting sun's narrative (diēgēmatikos), i.e. the ebbing sea's wanders.
Silence is sometimes also a mode of sublime, like the classical example of Ajax after his madness — using silence to imitate sublimity, when it's not fit to the subject matter, is equally bombastic as being garrulous, i.e. when keeping a lecture course one fears that their thinking isn't enough if stated in a straightforward fashion. Even if the substance of Plato's more youthful dialogues could be explicated in a series of lectures, the old whirlpool of 'mythōdēs' is here best left standing as it is — a sort of Protreptikos to interpret Plato. As such, it's better to leave this writing also here — Plato like a cloud gathering thunder, ready to strike lightning.