When he was seven, Gratian was made co-emperor with his father, Valentinian I. He became Augustus of the West when Valentinian died the next year. Gratian fought the Alemanni during the years 377-378. In 383, Magnus Maximus, proclaimed Augustus by his soldiers in Britain, crossed into France. His army met Gratian's near Paris, where Gratian's cavalry suddenly defected. He was captured and killed.