I just finished Jennifer A. Nielson's Mark of the Thief.  Wow, what a great read!  Historical fiction, mixed with a little fantasy, equals an action packed book with lots of twists.  The book takes place in ancient Rome. Nic, a slave boy, finds Julius Caesar's bulla, and receives it's magic. So begins Nic's new life.  Most of Rome is after the bulla. Some are trying to kill him and others are offering help (and maybe also trying to kill him). Nic is trying to figure out who he can trust and how he can escape. This story is a whole new way to look at ancient Rome, it's gods, and of course, the gladiator ring.  I highly recommend this book :)