Below is the larger quote from Plato's "The Criteas." This is an incomplete work, the famous one where Plato begins the re-telling of the story of Atlantis. This is where most of today's Atlantean lore actually comes from. Curiously, the work, and the discussion of the mythical kingdom, is incomplete. Plato just cuts off in mid sentence.
The following is Plato's account of a conversation between the Greek historian Solon and an Egyptian priest who claimed (in 560 BC) that Egypt carried evidence of a secret history, wherein civilazation long forgotten ascended and fell, perhaps many times in the distant past. And we, in a time long before even Solon, and Plato, simply forgot what happened.
FROM PLATO'S THE CRITEAS
“O Solon, you Greeks are all young in your minds which hold no store of old belief on along tradition, no knowledge hoary with age. The reason is this. There have been, and will be hereafter, many and divers destructions of mankind, the greatest by fire and water, though other lessor ones are due to countless other causes.
Thus the story current also in your part of the world, that Phaethon, child of the Sun, once harnessed his father chariot but could not guide it into his fathers course and so burnt up everything on the face of the earth and was himself consumed by a thunderbolt – this legend has the air of a fable; but the truth behind it is a deviation of the bodies that revolve in heaven around the earth and a distruction, occurring at long intervals of things on earth by a great conflagration… Any great or noble achievement or otherwise exceptional event that has come to pass, either in your parts or here or in any place of which we have tidings, has been written down for ages past in records that are preserved in our temples; whereas with you and other people again and again, life has only just been enriched with letters and all other necessities of civilization when once more, after the usual period of years, the torrents from heaven swept down like a pestilence, leaving only the rude and unlettered among you.
And so you start again like children, knowing nothing of what existed in ancient times here or in your own country… To begin with, your people remember one deluge, though their were many earlier; and moreover you do not know that the noblest and bravest race in the world once lived in your country. From a small remnant of their seed you and all your citizens are derived; but you know nothing of it because the survivors for many generations died leaving no word in writing”.
From Plato’s The Criteas – Senior Priest to Solon at Sais, Nile Delta c560 BC.