Atlantis Fallen - The Heartstrike Chronicles, #1

A city hidden for five thousand years. A man so ancient his early history is lost to time. A woman who has nothing to lose.Lorhen, oldest and most ruthless of the immortal Timeless, put aside the sword long ago for a quiet life. But peace doesn't last forever, especially for a man whose age can be counted in epochs, and the mortal life he's built unravels as the Keepers, a society of historians who record Timeless lives, learn that he's been hiding in their midst.
Then an archaeologist's claims of finding Atlantis brings back millennia-old memories, and Lorhen is drawn unwillingly into intrigues aeons in the making-and deadly enough that he may yet face the heartstrike blow that will unleash his power on the world..