In short, Rome controlled virtually every known trade route in the world, and this gave them extraordinary economic power. But it came at great cost: It’s expensive to wage war. It’s even more expensive to maintain a huge empire.And in order to pay for it all, Septimius Severus resorted to heavily debasing the Roman currency. The purity of the denarius silver coin plunged from 83.5% down to just 55% during his rule.