Almost simultaneously with this important event, the Creoles from Santa Fe province crossed over into the wide plains which lie between the Parana and the Uruguay, and defeated the Charrua tribes who had kept the Spanish out of that region for one hundred and fifty years. Soon the gauchos were in possession of Entre Rios as far as the Uruguay. The Charruas east of the Uruguay could not prevent the gauchos from making their way across the river to build their cabins and ride the plains after cattle. The settlement of western Uruguay began, but, except Colonia and Soriano, no towns were founded. The half-Indian gauchos lived a semi-nomadic life and needed and received little help from the authorities in their constant fights against the Indians. Shortly after the foundation of Montevideo, a Portuguese expedition tried to recover the place, but it was found to be too strong to attack, and the party resolved to establish a town farther up the coast. Three hundred miles to the north-west is found the only opening into the great system of lagoons which stretches along the seaward side of Rio Grande do Sul, and at that strategic point the Portuguese, in 1735, built a fort and town. By the middle of the eighteenth century, the situation between Spain and Portugal in the whole region between the Plate, the Uruguay, and the sea had become very strained. Colonia was completely isolated and the Spaniards controlled all the rest of Uruguay's western and southern water-front. The Portuguese settlements in the seaward half of Rio Grande were prospering and multiplying, soon to furnish thousands of gauchos, as ready as any who rode the Argentine pampas to sally forth for war or plunder. The territory which the Jesuits had held for more than a century on the east bank of the Upper Uruguay lay directly back of these Portuguese settlements and was more easily accessible therefrom than from Montevideo. In 1750 Spain agreed to exchange the Seven Missions for Colonia. The Portuguese promptly took measures to secure the ceded territory, attacked the Indian villages, and massacred or drove off most of the inhabitants. The Jesuits vigorously protested, and outraged Spanish public opinion demanded the abrogation of the treaty, so a few years later the desolated territory was restored to Spanish possession and Colonia remained Portuguese.