This was a neglect in Agricola occasioned probably by a limited command; and it was not rectified by boundless authority in Severus.

The Caledonians again resumed their arms, and renewed their ravages on the Roman frontier.

Severus died before he could take any new measures; and from his death there is an almost total silence concerning the affairs of Britain until the division of the Empire.
Had the unwieldy mass of that overgrown dominion been effectively divided, and divided into large portions, each forming a state, separate and absolutely independent, the scheme had been far more perfect.

Though the Empire had perished, these states might have subsisted; and they might have made a far better opposition to the inroads of the barbarians even than the whole united; since each nation would have its own strength solely employed in resisting its own particular enemies.

For, notwithstanding the resources which might have been expected from the entireness of so great a body, it is clear from history that the Romans were never able to employ with effect and at the same time above two armies, and that on the whole they were very unequal to the defence of a frontier of many thousand miles in circuit.
But the scheme which was pursued, the scheme of joint emperors, holding by a common title, each governing his proper territory, but not wholly without authority in the other portions, this formed a species of government of which it is hard to conceive any just idea.