of Africa, the equestrian province of Roman Egypt was an exception to the general rule of legions only being stationed in imperial provinces. Egypt was not a normal province; it was considered the personal possession of the Emperor, and its governor, the praefectus Aegypti, was considered the hold the highest ranking equestrian post during the early Empire. Later, the post would fall second to that of the praetorian command, but its position remained highly prestigious. Though the practice of appointing equestrians to help manage provinces officially began with Augustus, governors from years before had appointed procurators to help them govern. However, it was not until the reign of Claudius that these procurators received the powers of a governor. Procurators were civilian officials, unlike prefects. It is important to note that procurators were not magistrates, so did not possess imperium, and merely exercised the Emperor’s, or governor's, authority with his approval. Late imperial governors The provincial governors were the most important officials in the Roman administration for it was they who were responsible for tax collection, justice in the first instance, and public order in the first instance. They received, from the prefectures, the tax demands three times a year, which they circulated to the municipalities. Under the Dominate, the Emperor Diocletian began in AD 293 reforms of the provincial administration that were completed under the Emperor Constantine the Great in 318. Diocletian set up twelve dioceses (later several were split), originally two to four for each of the four co-emperors under the short-lived Tetrarchy (two senior Augusti, each above a Caesar), each governed by a vicarius ('vicar') who acted on behalf of the praetorian prefect. Each diocese comprised several Roman provinces (known in Greek as eparchies), each under the authority of a provincial governor, whose title varied from province to province (the range of titles includes republican relics such as proconsul, as well as novelties such as corrector provinciae, moderator provinciae, and praeses provinciae). Although the vicar's authority was supreme within his diocese, he was under the authority of praetorian prefect whose power he partook of the emperor himself. Constantine completely removed the governors' military commands, a process begun under Diocletian. In those provinces where soldiers were stationed, the dux (Latin for leader) commanded border military units. Some duces commanded units in several provinces: they were watched by the diocesan vicars. Field units were commanded by a comes ('companion', whence