A portion of one of the expeditions he despatched, under Juan de Ayolas,
pushing up the Paraguay, is said to have reached the south-east
districts of Peru, but while returning laden with booty, was attacked by
the Payagua Indians, and every man perished. The other portion, which
had stayed behind as a reserve under Domingos Irala, had better
fortunes. Finding their comrades did not return, Irala and his
companions determined to descend the river, and on their downward
journey opposite the mouth of the river Pilcomayo, finding a suitable
site for colonizing, they founded (1536) what proved to be the first
permanent Spanish settlement in the interior of South America, the
future city of Asuncion (15th August 1536).