I've long been recommending The Inheiritance Trilogy by Jennifer Nielsen, and I'm pleased to find that her new series The Praetor War is starting out with similarly strong writing and characters.
The Mark of the Thief will appeal to fans of Percy Jackson, as it brings together Roman history and Nielsen's own brand of magic. Our hero, Nic, is a Roman slave working in the mines outside of Rome. When a cave rumoured to contain the treasure of Julius Caesar is unsealed, Nic finds himself in possession of two things: Caesar's bulla, an amulet given to the emperor by the Gods, and a new mark on his shoulder, that of the Divine Star. Both contain magic that many Romans would kill for.
Incoporating both the beauty and the brutality of Ancient Rome, The Mark of the Thief is an adventurous tale and a fine follow-up to The Inheritance Trilogy. Highly recommended for all, but particularly for kids aged 10 to 14.