Falling Sky - Garry Disher

AD 265, Gaul - The Roman Empire is on the brink. Emperor Gallienus has amassed a huge army across the Alps to seize back the mountains from the usurper Posthumus. War has come. Ballista and his cavalry are on the frontline, battling in the most brutal of conditions. But if he is to survive the campaign and finally retire to his beloved Sicily, it's not just the battlefield he needs to navigate. As he and Praetorian Prefect Volusianus lay siege to Posthumus' armies, it becomes clear the greatest threat to Ballista's life might just come from within his ranks. After all, Volusianus has shown he will go to any distance for his own ends. Is Ballista just another pawn in his game?