The Last Roman: Honour by David Donachie

Justinian, a paranoid leader, desperately wants the lost provinces returned to his rule but must first dispatch his brave general, Belisaurius, to fight the Persians in the East. Justinian grows concerned that Belisaurius will grow successful and courageous in his feats, thus becoming a threat to his power and person. He subsequently dispatches him on a near-impossible mission to North Africa to take back from the Vandals what was once ancient Carthage. Meanwhile back in Constantinople, Marcus Donatus has found favor with Empress Theodora, wife of Justinian, in the hopes of being able to influence Justinian himself.
Binding: Paperback / softback