Complex sentence: Gennadius of Massilia wrote that Vincent died during the reign of Roman Emperor Theodosius II in the East and Valentinian III in the West, therefore, his death must have occurred in or before the year 450.
Split into simpler sentences: Gennadius of Massilia wrote that Vincent died during the reign of Roman Emperor Theodosius II in the East and Valentinian III in the West. Therefore, his death must have occurred in or before the year 450.