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_.