I should point out that even surface structures, exposed only to air and weather, also deteriorate considerably in a couple thousand years, and the sea is a considerably more hostile environment.
Well the prologue would be the history part. The actually novel will take place in the future. So I have to make the prologue believable.
Yuck, god no. It probably be more like someone's diary or something. Something far more interesting then that. Yuck, infodump prologues are the worst. I put myself to sleep while writing it.
Yes, and part of every "gentleman's" education included a large chunk of the "Classics," i.e. old Greek and Roman writings. Atlantis would actually be a very apropos name for them to think up themselves.