The Edge of the Empire by Kathy Lee
Having survived a disastrous battle, slavery, and the great fire of Rome, Bryn is ready to return to one of the most dangerous and uncivilised countries in the Empire: Britain! Although he has begun to love his life in Rome, Bryn is still a Briton at heart. He wants to know what happened after the great battle and if Conan, his brother, ever made it home. Taking his friends with him, Bryn discovers that his homeland is not as he left it. And a new threat is looming: a second rebellion is being planned. Will it bring ruin to the people?