[Paul R.]

From everything I’ve been able to find so far, sea levels have been pretty stable over the last 3000 years, and around 500 AD especially. There have been some periods of slight rises, but nothing to put a city underwater as seen in the photos @ the link. I’d guess at subsidence during a large seismic event. The Mediterranean region is very active...

http://science.nationalgeographic.com/science/earth/the-dynamic-earth/anatolian-history/#page=1

[Windflier]

I’d guess at subsidence during a large seismic event.

You know, that possibility also occurred to me. I'll bet that was what did it.

[Bernard Marx]

I’d guess at subsidence during a large seismic event.

Me too. With the African and Arabian Plates being subducted under the European Plate, conditions exist for many events like that over geologic time.