Masters of Rome by Robert Fabbri
Rome, AD 51: After eight years of resistance Vespasian captures Rome's greatest enemy, the British warrior Caratacus. But even Vespasian's victory cannot remove him from politics. Emperor Claudius is a drunken fool and Narcissus and Pallas, his freedmen, are battling for control of his throne. Separately, they decide to send Vespasian east to Armenia to defend Rome's interests.
Rumours abound that Claudius' wife Agrippina is involved in a plot to destabilise the East. Meanwhile, a new Jewish cult is flourishing and its adherents refuse to swear loyalty to the Emperor. In Armenia, Vespasian is captured. Immured in the oldest city on earth, how can he escape? And is a Rome ruled by Agrippina any safer than a prison cell?
THE FIFTH INSTALMENT IN THE VESPASIAN SERIES