Years ago I read a series (I think it was a trilogy) where there were users of magic in a civilization in the Mediterranean basin before it became a sea. About all I can remember is that the civilization got wiped out when the barrier between the Mediterranean basin and the Atlantic ocean was breached and the ocean waters rushed in and flooded the basin. I have a vague recollection that the breach wasn't natural, that someone broke the barrier on purpose, but I'm not certain about that.