But as the sphere of conquest widened, another economic phase supervened. Where newly conquered territory was too distant to tempt any save the poorest citizens, or to be directly utilised by the rich, it could still be made _ager publicus_ and rented to its own inhabitants; and the collection of this and other exactions from subject provinces gradually grew to be a main source of Roman wealth. For the mere cattle-looting of the early days there was substituted the systematic extortion of tribute. "In antiquity conquest meant essentially the power to impose a tribute upon the conquered";[170] and "until the time of Augustus the Romans had maintained their armies by seizing and squandering the accumulated [bullion] capital hoarded by all the nations of the world."[171] Meanwhile the upper classes were directly or indirectly supported by the annual tribute which from the time of the conquest of Greece was drawn solely from the provinces. Paulus Emilius brought from the sack of Hellas so enormous a treasure in bullion, as well as in objects of art, that the exaction of the _tributum_ from Roman citizens, however rich, was felt to have become irrational; and henceforth, until Augustus re-imposed taxation to pay his troops, Italy sponged undisguisedly on the rest of the Empire.[172] Cæsar's expeditions were simply quests for plunder and revenue; and the reason for his speedy retreat from Britain, for which there have been framed so many superfluous explanations, is plainly given in the letter of Cicero in which he tells of the news sent him from Britain by his brother--"no hope of plunder."[173] But the supreme need was a regular annual tribute, preferably in bullion, but welcome as corn. On the one hand the exacted revenue supported the military and the bureaucracy; on the other hand, the business of collecting taxes and tribute was farmed out in the hands of companies of _publicani_, mainly formed of the so-called knights, the _equites_ of the early days; in whose hands rich senators, in defiance of legal prohibition, placed capital sums for investment,[174] as they had previously used foreigners, who were free to take usury where a Roman was not. Of such money-makers Gallia Provincia was already full in the days of Cicero.[175] Roman administration was thus a matter of financially exploiting the Empire in the interest of the Roman moneyed classes;[176] and the ruthless skill with which the possibilities of the situation were developed is perhaps even now not fully realised. The Roman financier could secure a tribute upon tribute by lending to a subject city or State the money demanded of it by the government, and charge as much interest on the loan as the borrowers could well pay. We know that the notoriously conscientious Brutus, of sacred memory, thus lent, or backed a friend who lent, money to tribute-payers at 48 per cent., or at least demanded 48 per cent. on his loans, and sought to use the power of the executive to extort the usury.[177]