The year is 270 AD. A string of inept emperors and usurpers vying for power has led the Roman Empire into near-total economic collapse. This is its gravest crisis yet. Eager to capitalise on Rome's instability, barbarian tribes gather like a storm on the borders, to plunder the riches of civilisation. To the east, the Sassanids set out on a grand conquest that culminates with an assault against Roman lands. They are held back only by a staunch defence led by Palmyra. Queen Zenobia holds fast ...