 At Mediolanum ( Milan , Italy ) in July 285 , Diocletian proclaimed Maximian as his co @-@ ruler , or Caesar . The reasons for this decision are complex . With conflict in every province of the Empire , from Gaul to Syria , from Egypt to the lower Danube , Diocletian needed a lieutenant to manage his heavy workload . Historian Stephen Williams suggests that Diocletian considered himself a mediocre general and needed a man like Maximian to do most of his fighting . 
