About this time negro slaves were first introduced from Africa into the provinces of the River Plate. This measure had been originally urged by the famous Father Bartolomé de las Casas with a view of augmenting the local force of labour, and thus of alleviating the condition of the aboriginal races that in many parts were becoming exterminated on account of the excess of toil imposed upon them. This state of affairs, as a matter of fact, did not obtain in the Banda Oriental, where Indian and Spaniard stood entirely apart. Nevertheless an influx of negroes occurred in the province, and--though nothing can be said in favour of the morality of the proceeding--there is no doubt that, once arrived, their presence tended to benefit the industries of the land. The period now was one of considerable unrest throughout the Spanish main. For some while the adventurers of other nations, seeking a share in the great riches of the South American provinces, had been knocking loudly at the gates that remained closely barred to them. Privateering and raids upon the coast had become more and more frequent, while the Spanish galleons, in continuous dread of attack, only put to sea for the purpose of long voyages in imposing numbers and beneath weighty escort. The River Plate, owing to the practical absence of the mineral traffic from its frontier, suffered far fewer depredations than fell to the lot of the gold and silver bearing countries to the north. Yet the homelier riches of the pastoral districts were becoming known and appreciated to a certain extent. In consequence of this the waters of the River Plate from time to time had many unwelcome visitors. Privateers of all nationalities, although their enforced ignorance of the navigation forbade them to penetrate for any distance up the waters of the great streams themselves in the face of local opposition, harassed the coast-line, and occasionally landed in more or less formidable parties. One of the most notable of these was a French adventurer of the name of Moreau, whose buccaneering ideas were considerably in advance of those of the majority who were wont to harry these particular districts. Moreau's plan of campaign, in fact, savoured rather of regular warfare than of the more usual methods of the rapid raidings and retreats. Thus in 1720 he disembarked with a body of men and four cannon at Maldonado, where he fortified himself, and began to amass a great store of hides. Surprised by the Spaniards, he was forced to take to his ships in haste, with the loss of his guns and of his stock-in-trade. A few months later the Frenchman returned, accompanied this time by a force of over a hundred well-armed men, and prepared to settle himself for an extended stay in the country. Curiously enough, it appears to have been the unfortunate Moreau's fate to reverse the fighting rôles of the buccaneer and local resident, since, instead of surprising others, it was he who was caught unawares on either occasion.