but they had standing grievances against the Empire. Any political
crisis suggested to them the idea of a mutiny led by the general,
sometimes to obtain arrears of pay and donatives, sometimes to put their
nominee upon the throne. The evil was an old one, dating from the latter
days of the Republic, when Marius, in the interests of efficiency, had
made military service a profession. But it was aggravated under the
successors of Diocletian, as the barbarian element in the armies
increased and the Roman element diminished. Its worst effects appeared
in the years 406-407. The German inroads upon Italy and Gaul were then
followed by the proclamation of military usurpers in Britain and on the
Rhine; the Roman West was divided by civil war at the very moment when
union was supremely important. Hence the strange spectacle of the
Visigoths, still laden with the spoils of Rome, entering Gaul by
invitation of the Empire to fight against imperial armies.

The problem of numbers had been earlier recognised, but not more
adequately met. Diocletian is said to have quadrupled the armies, and in
the fourth century they were far larger than they had been under Julius
and Augustus; Constantine had revised the scheme of frontier-defence to
secure the greatest possible economy of men. Still, under Honorius, we
find that one vital point could only be defended by withdrawing troops
from another. The difficulty of increasing the numbers was twofold.
First, the army was mercenary, and taxation was already strained to the
point of diminishing returns. Secondly, it was difficult to raise
recruits among the provincials. The old principle of universal service
had been abandoned by Valentinian I (364-375); and although compulsory
levies were still made from certain classes, the Government had thought
fit to prohibit the enlistment of those who contributed most to
taxation. Every citizen was legally liable for the defence of local
strongholds; but the use of arms was so unfamiliar, the idea of military