Battle of the Milvian Bridge

Constantine defeated his rival Maxentius at the Milvian Bridge over the Tiber River, just outside Rome. According to legend, Constantine saw a cross of light in the sky with the words 'In this sign, conquer' before the battle and ordered his soldiers to mark their shields with the Christian chi-rho symbol. Maxentius drowned in the Tiber while fleeing. The victory led Constantine to issue the Edict of Milan, legalizing Christianity throughout the Roman Empire.