Among those who escaped to Buenos Aires was one destined to be the founder of Uruguayan nationality. This was Jose Artigas, then captain of guerrilla cavalry. Although born in Montevideo he had lived the life of a gaucho from boyhood, and since 1797 had been a leader of the gaucho bands who were continually fighting the Rio Grandenses. He happened to be in Colonia on the occasion of Elio's declaration of war against the Creoles and at once fled to Buenos Aires. The junta there gave him a lieutenant-colonel's commission and some substantial help. The gauchos of the south-eastern part of Uruguay had meanwhile risen against the Spanish governor, and within a few weeks Artigas was back on Uruguayan soil at the head of a considerable force, while all around him bands of gauchos under other chiefs were preparing to resist the Spaniards. His bravery, energy, and good luck in the field, and his ruthless maintenance of discipline, gave him an ascendancy over all the others. In April, 1811, Belgrano, the chief general of Buenos Aires, arrived with re-enforcements. Shortly after, a Spanish detachment, which had reached the western part of Uruguay, was captured, and the gaucho leaders advanced almost to the walls of Montevideo. A force of one thousand Spaniards started out to meet them and, on the 18th of May, met with complete defeat at the battle of Las Piedras. For this victory Artigas was promoted by the Buenos Aires Junta, and became the greatest military figure on the patriot side. With a considerable army of gauchos from both banks of the Uruguay and of patriots from Buenos Aires he began a siege of Montevideo. The siege, however, did not last long. The great expedition sent by the patriots to Bolivia was overwhelmingly defeated in the battle of Huaqui, and the Buenos Aires Junta, horribly alarmed for their own safety, ordered all the troops under their control to return and help defend that city. At the same time a Portuguese army advanced from Brazil with the avowed purpose of saving Montevideo from being lost to Spain, but really to take possession of Uruguay for King John's own benefit. Artigas was compelled to retire to the Argentine, and Uruguayan historians say that on his long retreat to the Uruguay River he was accompanied by practically the whole rural population of the country. The semi-nomadic habits of the gauchos made such a migration easy, and they quickly found new homes on the opposite shore in Entre Rios, whence it would be easy to return as soon as the Portuguese troops retired.