For more mature readers, perhaps 16 and older, due to some mature content, I would highly suggest The Mark of the Lion Trilogy, which includes the books A Voice in the Wind, Echo in the Darkness, and As Sure as the Dawn. They are written by Francine Rivers.
These books will catapult you back in time to the days of Rome, where Coliseums were the main attraction, Gladiators were the famed heroes of the land, and the lives of the wealthy could match any modern day soap opera. The story follows a young Jewish slave girl who struggles to cling to life, and do what is right in a land where morals and goodness are scoffed and persecuted.