Mark of the thief trilogy

When Nic, a slave in the mines outside of Rome, is forced to enter a sealed cavern containing lost treasures of Julius Caesar, he finds himself in possession of an ancient amulet filled with magic once reserved for the Gods, and becomes the center of a conspiracy to overthrow the emperor and destroy Rome.

Trouble has a way of seeking out Nicolas Calva, and it's not likely to leave him alone any time soon. With Caesar's magic bulla, the Malice of Mars, and the possibility of a Jupiter Stone in play, all the powers of Rome are circling Nic. He'll have to maneuver his way through scheming government officials and reawakened magical beasts to save the Empire. Can he manage to keep his friends and family safe, claim his own freedom once and for all, and...