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.
After this encounter famine seemed to stare the followers of Mendoza in the face, and an expedition sent up the river in search of food was everywhere met with hostility. Mendoza now determined to proceed up the stream, and on an island he found an interpreter in one of the followers of Cabot. _Buenos Ayres_ was meanwhile partly relieved by the return of an expedition that had been sent to procure provisions from the coast of _Brazil_. This was the extent to which the bright visions of Mendoza were destined to be realized. Tortured in body and broken in spirit, the knight left the scene of his misfortunes. On his homeward voyage he was still pursued by hunger, and his reason gave way before death came to his relief.
Mendoza had resigned his powers to his lieutenant, Ayolas, who ascended the _Paraná_ and reached the _Paraguay_, there losing one of his ships. Those whom it had conveyed proceeded by land, and encountered a tribe in some respects civilized. The _Carios_ possessed maize and the sweet potato, and in their farms were found ostriches, sheep, and pigs. Their capital was surrounded by stakes. The tribesmen offered the invaders provisions on condition of their departing. This not being accepted, a fight ensued, and the natives fled. Ayolas then founded a city, in which he took to himself, as we are told, seven wives, permitting two to each of his followers. The city was called _Asuncion_.