The Eastern Roman armies under Constantius II defeated those of the usurper Magnentius at the Battle of Mursa Major. Constantius II: Constantius II was Roman emperor from 337 to 361. His reign saw constant warfare on the borders against the Sasanian Empire and Germanic peoples, while internally the Roman Empire went through repeated civil wars, court intrigues, and usurpations. His religious policies inflamed domestic conflicts that would continue after his death. September 28, 351. Wiki link