Few parts of the plateau escaped coming under Spanish rule, but the white conquerors, like their Inca predecessors, stopped short when they reached the dense forests and steep valleys, eroded by wildly rushing rivers, which cover the eastern slope of the great mountain region. Down these terrific gorges no progress was made, and only occasionally did some devoted priests manage to establish a mission among the intractable Indians who inhabit the open prairies interspersed among the beautiful forest-covered plains drained by the tributaries of the Madeira. The roads the Incas had built to the Pacific continued even in Spanish times to be the only practicable way of communication between Bolivia and the outer world. Transportation over the steep and tedious route from Potosi to La Paz, thence around Titicaca, and along the high valleys of southern Peru to the beginning of the tremendous descent to Lima, was too expensive to permit any export except of the precious metals. To the south there was a somewhat easier route to the valleys of north-eastern Argentina, into which the Spaniards had spread within a few decades after the discovery of Potosi, and whence food and pack animals were drawn for the mining regions. Spanish law forbade the use of the Atlantic ports at the mouth of the Plate, and for more than two centuries Bolivia continued under both administrative and commercial subordination to Lima. Jesuit missionaries arrived in Bolivia within twenty-five years after Loyola had founded the order. They established an important mission on the banks of Lake Titicaca in 1577, and five years later introduced the printing-press in order to distribute among their proselytes grammars and catechisms in the native tongues. In the seventeenth century they succeeded in penetrating down the eastern slope of the Andes and across the great central plain to the outlying hills of the Brazilian mountain system where they established several missions among the Chiquitos Indians. They even reached the grassy prairies which lie three hundred miles north of the inner angle of the great plateau, converted the Mojos, and taught them to herd cattle. But in the forests and along the base of the Andes the fierce tribes held their own as they had against the Incas and as they have continued to do against the Spanish-Americans to this day.