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 service as a national duty was so far forgotten, that Stilicho, when the barbarians were actually in Italy, preferred the desperate measure of enlisting slaves to the obvious resource of a general call to arms. We find ourselves here confronted with a social malady which was more than an economic weakness. The Empire was, no doubt, a complex and expensive form of government superimposed upon a society which stood at a rudimentary stage of economic development. Barbarous methods of taxation and corrupt practices among the ruling classes had aggravated the burden to such a degree that the municipalities of the provinces were bankrupt, and the middle-class capitalist was taxed out of existence. For this and other reasons the population of the older provinces was stationary or declining. But there was still much wealth in the Empire; and the great landowners of the provinces could raise considerable armies among their dependants when they saw fit to do so. The real evil was a moral evil, the decay of civic virtue.