The fortified town of Colonia, on the north bank of the Uruguay River, represented one of the chief bones of contention. Its possession constituted a strategic advantage of no small importance, and Spanish and Portuguese flags waved alternately over its shattered ramparts. The situation was accentuated by the characteristics of the inhabitants of the Portuguese city of Sao Paolo. These people, who lived in the town loftily placed upon its rock, had acquired for themselves, almost from the inception of the colony, a somewhat sinister and reckless reputation. The Portuguese and half-breeds here, their vigour unimpaired by a temperate and bracing climate, would sally out to the west and to the south on slave-raiding expeditions, which they conducted with extraordinary ferocity and enterprise. Matters of boundaries and frontiers possessed no interest whatever for these Paolistas or Mamelucos, by which latter name the swashbuckling members of this community were better known. [Illustration: FRANCISCO PIZARRO. The Conqueror of Peru. _From an engraving after the original portrait in the Palace of the Viceroys at Lima._ _A. Rischgitz._] In the first instance, these forays were responsible for comparatively little friction, since the number of Indians near at hand was as plentiful as the neighbouring white men were rare. When the nearer land became depopulated, however, it began to be necessary to extend the expeditions farther afield from Sao Paolo, and it was then that the Mamelucos came into contact with the growing numbers of the Spanish settlers, and with the Indians who now resided beneath the protection of the Spanish power. When the Jesuit missionaries arrived in Northern Uruguay and in Southern Paraguay their advent had the effect of embittering the feud between the frontiersmen; for the Jesuits, forming the Indians into companies of their own, withdrew them still farther from the onslaughts of the Paolistas. These latter determined at all costs to capture and to drive back their gangs of slaves, became more and more emboldened, and pushed forward to the south and west well into the Spanish territories, harrying the missionary settlements, and laying waste the countryside. For years the Guarani Indians, unarmed, were helpless in the face of such attacks. Eventually, however, the influence of the Jesuits obtained permission from the Court of Spain for these latter to be provided with firearms, and after this the Indian regiments, trained and disciplined, offered such effective resistance to the Mamelucos that these were forced to cease their slave-raids.