In the second and third centuries, in order to maintain control and improve administration of the expanding Roman Empire, various schemes to divide the work of the Roman Emperor by sharing it between individuals were tried generally involving a division of labor between East and West. Each division was a form of power-sharing (or even job-sharing), for the ultimate imperium was not divisible and therefore the empire remained legally one state—although the co-emperors often saw each other as rivals or enemies. Emperor Diocletian created the tetrarchy to guarantee security in all endangered regions of his Empire. He associated himself with a co-emperor (Augustus), and each co-emperor then adopted a young colleague given the title of Caesar, to