600 to 700 AD when the ground sank into the sea, odd that they had no maps of it's former location. There is a missing sea port in India that used to be the gateway for Roman Empire trade with that country that I hope is discovered.
So cool, and one of the few reasons I think a bigger urgency should be put on our own planet, than space exploration (or at least the same amount of urgency).....we have depths, organisms, animals and cities that we havent even discovered yet on the planet we are inhabiting. Would be nice to explore it some more!