The praefecti praetorio, 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 praefectus praetorio of Gaul.  The military was divided nearly in the same manner; and it was placed under officers also of a new creation, the magistri militiae.  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.

But Constantine made a much greater change with regard to religion by the establishment of Christianity.  At what time the Gospel was first preached in this island I believe it impossible to ascertain, as it came in gradually, and without, or rather contrary to, public authority.  It was most probably first introduced among the legionary soldiers; for we find St. Alban, the first British martyr, to have been of that body.  As it was introduced privately, so its growth was for a long time insensible; but it shot up at length with great vigor, and spread itself widely, at first under the favor of Constantius and the protection of Helena, and at length under the establishment of Constantine.  From this time it is to be considered as the ruling religion; though heathenism subsisted long after, and at last expired imperceptibly, and with as little noise as Christianity had been at first introduced.

[Sidenote:  A.D. 368.]

In this state, with regard to the civil, military, and religious establishment, Britain, remained without any change, and at intervals in a tolerable state of repose, until the reign of Valentinian.  Then it was attacked all at once with incredible fury and success, and as it were in concert, by a number of barbarous nations.  The principal of these were the Scots, a people of ancient settlement in Ireland, and who had thence been transplanted into the northern part of Britain, which afterwards derived its name from that colony.  The Scots of both nations united with the Picts to fall upon the Roman province.  To these were added the piratical Saxons, who issued from the mouths of the Rhine.  For some years they met but slight resistance, and made a most miserable havoc, until the famous Count Theodosius was sent