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. Gratian was captured and killed.