text: The Western Roman Empire was the western half of the Roman Empire after its division by Diocletian in 285 ; the other half of the Roman Empire was the Eastern Roman Empire , commonly referred to today as the Byzantine Empire .
simplified: The Western Roman Empire was the western half of the Roman Empire , from its division by Diocletian in 286 ; the other half of the Roman Empire became known as the Eastern Roman Empire , today widely known as the Byzantine Empire .