The reign of Marcus Aurelius was marked by military conflict. In the East, the Roman Empire fought successfully with a revitalized Parthian Empire and the rebel Kingdom of Armenia. Marcus defeated the Marcomanni, Quadi, and Sarmatian Iazyges in the Marcomannic Wars; however, these and other Germanic peoples began to represent a troubling reality for the Empire. He modified the silver purity of the Roman currency, the denarius. The persecution of Christians in the Roman Empire appears to have increased during Marcus' reign, but his involvement in this is unknown. The Antonine Plague broke out in 165 or 166 and devastated the population of the Roman Empire, causing the deaths of five million people. Lucius Verus may have died from the plague in 169.