Romulus and Fabiola are twins, born into slavery after their mother is raped by a drunken nobleman. At thirteen years old they are sold - Romulus to gladiator school, Fabiola into prostitution, where she will catch the eye of one of the most powerful men in Rome. Tarquinius is an Etruscan, a warrior and soothsayer, born enemy of Rome, but doomed to fight for the Republic in the Forgotten Legion. Brennus is a Gaul, his entire family killed by the Romans, and he rises to become one of the most famous and feared gladiators of his day.

The lives of these characters are bound and interwoven in an odyssey which begins in a Rome riven by political corruption and violence, but ends far away, at the very border of the known world, where the tattered remnants of a once-huge Roman army - the Forgotten Legion - will fight against overwhelming odds, and the three men will meet their destiny.