Roman troops file in neat lines over raging rivers and trackless mountains. They crush barbarian forces in battle after battle, leaving fields of corpses in their wake. Villages burn, captives weep – and the lonely figure of the philosopher-emperor leads his legions to victory. So the spiraling reliefs of the Column of Marcus Aurelius, subject of the seventh episode in our History of Rome, represent the brutal conflict that turned back the first wave of the barbarian invasions.