The two earliest explorers of the _Plata_ had been professional navigators; the commander of the third great expedition to that region was a courtier and a wealthy knight. _Don_ Pedro de Mendoza, no doubt attracted by the name of the Silver Stream, undertook to plant the Spanish race on its shores on the following conditions, namely: That the region extending from the _Plate_ to the Straits of _Magelhães_, a barren territory, was to be under his government; that he should pursue his way by peaceful or by warlike means across the continent until he should reach the ocean; that he was to be entitled _Adelantado_, and to receive a salary of four thousand ducats; that he was to be perpetual _Alcalde_ of one of three forts which he was to establish; that to his heirs should be reserved the post of first _Alguazil_ of the town where he should fix his residence; and that, should he capture another Montezuma or Atahualpa, he and his soldiers should receive two-thirds of the royal ransom. As a commentary on these ambitious views, Mendoza likewise took with him eight priests to teach and spread the unselfish doctrines of Christianity. His force consisted of some two thousand men with one hundred horses. Touching on his way at _Rio de Janeiro_, he thence proceeded along the coast and up the river _Plata_ to the distance of one hundred miles. The flat southern shore was then in the possession of the _Quirandis_, a tribe which has long since disappeared before civilization. The green plains, unclothed by woods and unbroken by hills, displayed no natural feature from which the knight might derive a name for his town; but as the climate seemed of the best, he resolved to call it _Buenos Ayres_. [Sidenote: 1534.] For some time the tribesmen supplied the invaders with food; but, with the fickleness of barbarians, they one day sent back their messengers mauled and empty-handed. This was a _casus belli_. The brother of Mendoza marched against the natives with three hundred foot-soldiers and thirty horsemen. Heretofore Spanish cavalry had, in their encounters with American aborigines, invariably been successful. The mailed warriors of Cortez or Pizarro had turned the scale of victory on many a day; but the cavaliers who charged with Diego Mendoza were met with a weapon now used for the first time against the horse and his rider. _Bolas_, or balls of stone, attached to each other, three together, by strips of hide, were hurled at the advancing centaur, which, entangled and stopped, came headlong to the earth. _Don_ Diego and some horsemen were killed, and twenty footmen met their death in covering the retreat of their mounted comrades. The discipline of the infantry, however, enabled them to remain masters of the field.