The influx of Spanish adventurers and officials also stimulated the extension of the system of agricultural encomiendas--that is, the grants of large tracts of land with the privilege of enslaving the Indian occupants. Sheep were introduced from Spain within twenty years of the conquest, and immense herds belonging to the Spanish proprietors and tended by Indian slaves soon covered the vast pasture grounds which are found even on the higher and colder portions of the plateau. Horses had come with the first conquerors and the breeding of mules flourished, especially in Cochabamba, the great agricultural centre which was founded in 1573, as well as in Charcas and the far southern districts of Tucuman. Cattle spread quickly over these same regions, and their beef, maize, mules, and horses found a good market in the mining districts. By the year 1580 the Spanish colonial system affecting the natives had been perfected, codified, and put into general operation. The whole country was divided into about thirty districts, each governed by a corregidor who in theory was controlled by a complicated and carefully drawn system of regulations, but who in practice was a petty tyrant against whom the white Creoles had little chance of redress, and who held the Indians absolutely at his mercy. The regulations framed by the distant viceroy at Lima for the protection of the natives were evaded by the corregidors, intent solely on extorting money from the poor creatures committed to their charge. Encomiendas had nominally been abolished, but landed proprietors still exercised the right to exact tribute from the Indians on their estates and great numbers were forced to serve as life servants under various pretexts. Those Indians who retained a semblance of freedom obeyed their own caciques, who were often the descendants of the royal Inca family. The principal duty for which the Spaniards held these chiefs responsible was the collection of the head-tax in their respective villages. The letter of the law required a seventh of the adult male population to work for the benefit of the Government, and in practice this resulted in an unlimited farming out of Indians as slaves to the rural proprietors. As much as possible the Indians retired to their villages to escape the notice of the officials, hoping to find under their own caciques a measure of security and a chance to live in modest poverty. Misrule, slavery, labour in the mines, neglect of that intensive and government-directed agriculture which had alone rendered it possible to sustain the dense population of Inca times, decimated the Indians.