Clash of Lions by Anthony Riches

Rival emperors Severus (in the west) and Niger (in the east) continue to wreak havoc across the empire by pitting legion against legion in civil war. In what is a continuation from the previous novel, although you could certainly read this on its own, our battle-scarred heroes, Marcus Aquila, Dubnus, and their boss Scaurus are now working in the east to wipe out Niger's army of spies who are led by their arch enemy Sartorius, clearing a path for Severus's army. It's exciting stuff, albeit tinged with sadness after recent events. Nobody feels immortal (except perhaps Severus, who puts in some quite frightening cameos here) and the fighting is hard, even more so as Roman fights Roman. I love this series and have read every one. I'll read every one to come and may there be many of them.