The Chronicle of Sword and Sand, book 1: The desert of souls
Howard Andrew Jones2011

In 8th century Baghdad, a stranger pleads with the vizier to safeguard the bejeweled tablet he carries, but he is murdered before he can explain. Charged with solving the puzzle, the scholar Dabir soon realizes that the tablet may unlock secrets hidden within the lost city of Ubar, the Atlantis of the sands. When the tablet is stolen from his care, Dabir and Captain Asim are sent after it, and into a life and death chase through the ancient Middle East.

Stopping the thieves—a cunning Greek spy and a fire wizard of the Magi—requires a desperate journey into the desert, but first Dabir and Asim must find the lost ruins of Ubar and contend with a mythic, sorcerous being that has traded wisdom for the souls of men since the dawn of time. But against all these hazards there is one more that may be too great even for Dabir to overcome…