<P> To maintain control and improve administration, various schemes to divide the work of the Roman Emperor by sharing it between individuals were tried between 285 and 324, from 337 to 350, from 364 to 392, and again between 395 and 480 . Although the administrative subdivisions varied, they generally involved a division of labour 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 . </P> <P> In 293, emperor Diocletian created a new administrative system (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 share in their rule and eventually to succeed the senior partner . The tetrarchy collapsed, however, in 313 and a few years later Constantine I reunited the two administrative divisions of the Empire as sole Augustus . </P> <P> In 330, Constantine moved the seat of the Empire to Constantinople, which he founded as a second Rome on the site of Byzantium, a city strategically located on the trade routes between Europe and Asia and between the Mediterranean and the Black Sea . Constantine introduced important changes into the Empire's military, monetary, civil and religious institutions . As regards his economic policies in particular, he has been accused by certain scholars of "reckless fiscality", but the gold solidus he introduced became a stable currency that transformed the economy and promoted development . </P> <P> Under Constantine, Christianity did not become the exclusive religion of the state, but enjoyed imperial preference, because the emperor supported it with generous privileges . Constantine established the principle that emperors could not settle questions of doctrine on their own, but should summon instead general ecclesiastical councils for that purpose . His convening of both the Synod of Arles and the First Council of Nicaea indicated his interest in the unity of the Church, and showcased his claim to be its head . The rise of Christianity was briefly interrupted on the accession of the emperor Julian in 361, who made a determined effort to restore polytheism throughout the empire and was thus dubbed "Julian the Apostate" by the Church . However this was reversed when Julian was killed in battle in 363 . </P>

What year did constantinople become the capital of the roman empire