The year is AD255 - the Roman imperium is stretched to breaking point, its authority and might challenged throughout the territories and along every border. The most potent threat lurks far to the east in Persia, where the massing forces of the Sassanid Empire loom with fiery menace. There lies the far-flung and isolated citadel of Arete, facing out across the wasteland, awaiting the inevitable invasion. One man is sent to marshal the defences of this lonely city - one man to shore up the crumbling walls of this once indomitable symbol of Roman power - a man whose name itself means war, a man called Ballista. Alone, Ballista is called to muster the forces, and the courage, to stand first and to stand hard, against the greatest enemy ever to confront the imperium.