Atlantis, Xanadu, the City of Z.
Lost cities have captured our collective imagination for generations. One of the most celebrated was Heracleion - Egypt's main port in the time of the pharaohs.
According to legend it was an important place of knowledge, trade and religion...until it sank into the Mediterranean sometime in the 8th century, lost forever.
But then, something amazing happened. It was found.
Erin Burnett has the story.