The saga of the sunken Atlantis comes from Plato. Solon, who lived about 200 years before him, was supposed to have brought it from a journey to Sais in Egypt. He stayed there to gain knowledge of the past.
From the "most knowledgeable priests" he learned of an "incredible story" of which "neither he nor another Hellene knew the least." ... "The number of years since our state Egypt exists is indicated in our sacred Scripture for eight thousand years… I will now briefly tell you about your fellow citizens, the Athenians, who have lived nine thousand years ago the most beautiful feat done by them." This, the priest said to Solon.
The Athenians, from today's point of view, almost twelve thousand years ago, led a war against the overpowering Atlantis and they were victorious. Later on there came a time of tremendous earthquakes and flooding and "the army of the Hellenes sank on a bad day and in a terrible night under the earth, and in the same way the island of Atlantis was sinking into the sea."
Plato picked up the matter. The saga should be the central theme in his later work, planned as a speech contest between three savants. In the preliminary discussion of the competition, at the eve, the philosopher Socrates expressed the wish, that he would like to see, with the help of this old legend, how an exemplary organized little state, the Athenians, was capable to defeat the overpowering opponent, Atlantis. But as far as this Plato did not come in his report.
After the description of the city of Athens and the island of Atlantis, especially its great metropolis in every detail, Plato broke the whole speech contest. Since this time the enigmatic Atlantis has been searched in vain.
Can we be sure, that the twelve thousand years before our time are right? In the year 1829 the savant J.F. Champollion deciphered in an Egyptian tomb a text that put him a shock. "What I read so fluently distracts me more than anything I could imagine in my imagination ..." he writes in his diary. This text was written in a time when, according to scientific opinion, there were still no people in the world.
According to calculations based on the Bible, the Flood occurred in 2349 B.C. Before this time there were no people, as one believed. That means that until about 150 years ago, one looked at the Atlantis report quite differently from today. According to Plato's data, it was believed for about 2000 years, that there existed already highly cultivated people on earth for an infinitely long time before us.
After the aborted debating duel Plato wrote his last and longest work „Nomoi“. In the third chapter he comes back to the old legends and again he confirms, that they are really true. Quite similar to the Atlantis report, he wrote about highly developed people, who have perished in a deluge. „All tools….laboriously invented things... the art of state administration….and any other knowledge..." everything was lost in that time.
After that, this knowledge has been unknown to humans about thousand times thousands of years (millions of years). Thus Plato wrote in Nomoi 677 c, d.
Obviously, in dealing with the subject, he realized that this flood occurred not a few thousand years ago, but millions of years ago. Many finds prove that humans and dinosaurs lived on the earth at the same time. Plato wanted to hand down this sensation to the posterity.
Plato had to give up the plan to show the advantages of an ideal and well-organized state with help of the old legend. The Atlantis report was not suitable for this project. What can you know after millions of years about this ancient people? - Plato, therefore, broke the Atlantis report.
In Nomoi, he wrote only in general of a highly developed people that had perished millions of years ago in a deluge, without mentioning details. His chief interest was now to describe the survival of the few humans after the flood, shepherds who survived the catastrophe on high mountains. „Weak sparks of mankind rescued on the peaks of the mountains“ so Plato called them.
Summary : The knowledge of the highly developed people who sunk in the flood was unknown to their posterity millions of years. Only one or two thousand years before Plato's time the lost knowledge has been rediscovered, some of it just before his time. So you can read in „Nomoi 677, c and d“ (Plato lived about 400 B.C.)