The lost empire thread has a mention of Atlantis. I remember having read a book which stated that it was clearly considered as an allegory of Athenian society at the start it that it was only quite later (I remember less clearly that christianization was a factor) that people started to consider it more seriously.
Is that story (people started to consider the myth as history only a relatively long time after Plato, and the link of that believe with Christianity) based on facts? What would be a good source on the history of the myth?
The original mention is by Plato in Timaeus, and it's very brief. Then a couple of his students talk about it, but from there on is a series of speculations on the nature of what Plato mentions.
Is that based on facts?
Not likely. In the context in which it's mentioned, is as a counter of Plato's own Republic and it serves more as a point of comparison between systems, than an actual real place.