The perpetual wars had multiplied slaves; and the slaves added a new and desperate element to the social problem. It was the proof of the fatal lack in Rome of vital ethical feeling--or, let us say, of social science--that this deadly iniquity was never effectually recoiled from, or even impugned as it had been, before Aristotle, among the more highly evolved of the Greeks.[49] As wealth and luxury, pride and power accumulated, the usage of slave labour spread ever further and ate ever deeper into the population, brutalising alike the enslaved and the free. It was doubtless a partial recognition of this that motived, in Cicero's day, the large number of affranchisements of slaves (Wallon, _Hist. de l'Esclavage_, ii, 409). But fresh enslavements went on; the amelioration consisted in the brevity of the period of enslavement in cases of good conduct. And the evil was in the main a product of conquest. It is fairly established by Dureau de la Malle (_Écon. polit. des Romains_, 1840, vol. i, liv. ii, ch. 2) that down to the second Punic War Roman slaves were few. They would be for the most part _nexi_, victims of debt. As conquests multiplied prisoners, the class increased rapidly. Broadly speaking, the house servants were all slaves, as were the bulk of the shepherds in the great _latifundia_, the crews of the galleys, and many of the artisans. The total number has doubtless been greatly exaggerated, both in ancient and modern times, as has been the population of the imperial city. Athenæus is responsible for many wild estimates. (Cp. Letronne, as cited by Dureau, liv. ii, ch. 4.) Dureau arrives by careful calculation at an estimate of an Italian population of some five millions about the year 529 A.U.C., of whom some two and three quarter millions were free and some two and a quarter millions were slaves or _metæci_, aliens without political rights (i, 296). The population of Rome as late as Aurelian he puts at between 500,000 and 600,000 (i, 368). (See Prof. Bury's note in his ed. of Gibbon, iii, 308, for different views. Gibbon, Bunsen, and Hodgkin put the figure at about a million.) The exact proportion of slaves to free is not of the essence of the problem. A society with nine slaves for every eleven free was sufficiently committed to degeneration.