 The Spanish conquistador Juan de Ayolas (died c. 1537) may have first visited the site of the future city on his way north, up the Paraguay River, looking for a passage to the mines of Alto Perú (present-day Bolivia).Later, Juan de Salazar y Espinosa and Gonzalo de Mendoza, a relative of Pedro de Mendoza, were sent in search of Ayolas, but failed to find him.On his way up and then down the river, de Salazar stopped briefly at a bay in the left bank to resupply his ships.