Constantius, after he came to the purple, chose this island for his residence. Many authors affirm that his wife Helena was a Briton. It is more certain that his son Constantine the Great was born here, and enabled to succeed his father principally by the helps which he derived from Britain.
Under the reign of this great prince there was an almost total revolution in the internal policy of the Empire. This was the third remarkable change in the Roman government since the dissolution of the Commonwealth. The first was that by which Antoninus had taken away the distinctions of the _municipium_, province, and colony, communicating to every part of the Empire those privileges which had formerly distinguished a citizen of Rome. Thus the whole government was cast into a more uniform and simple frame, and every mark of conquest was finally effaced. The second alteration was the division of the Empire by Diocletian. The third was the change made in the great offices of the state, and the revolution in religion, under Constantine.
The _præfecti prætorio_, who, like the commanders of the janizaries of the Porte, by their ambition and turbulence had kept the government in continual ferment, were reduced by the happiest art imaginable. Their number, only two originally, was increased to four, by which their power was balanced and broken. Their authority was not lessened, but its nature was totally changed: for it became from that time a dignity and office merely civil. The whole Empire was divided into four departments under these four officers. The subordinate districts were governed by their _vicarii_; and Britain, accordingly, was under a vicar, subject to the _præfectus prætorio_ of Gaul. The military was divided nearly in the same manner; and it was placed under officers also of a new creation, the _magistri militiæ_. Immediately under these were the _duces_, and under those the _comites_, dukes and counts, titles unknown in the time of the Republic or in the higher Empire; but afterwards they extended beyond the Roman territory, and having been conferred by the Northern nations upon their leaders, they subsist to this day, and contribute to the dignity of the modern courts of Europe.