Constantine, again following Diocletian's lead, organized the Roman Empire into three praetorian prefectures late in his reign. These were based on the territories controlled by the four co-emperors of the Tetrarchy, two of whom, the senior Augusti, had been served by a praetorian prefect as something like a chief of staff. The three prefectures thus created were the prefecture of Gaul, the prefecture of Italy, Africa, and Illyricum (later divided by Constans in 347 or perhaps in 342/47), and the prefecture of the East, each being administered by an imperially-appointed Praetorian prefect. The prefect of each prefecture was the highest civilian officer, being subordinate only to the emperor(s). The prefect was the superior of the vicars and governors. He was the chief appellate judge, head of the administration of the prefecture, chief finance officer, and chief tax collector (though the collection was actually done at municipal and village levels).