Mendoza, Pedro de (pāˈħrō dā māndōˈthä) [key], b. 1501 or 1502, d. 1537, Spanish conquistador, first adelantado [civil and military governor] of Río de la Plata (present-day Argentina). After a military career in Europe, he received (1534) from Emperor Charles V a commission to conquer and colonize the Río de la Plata region. With 11 vessels and 1,200 men, he sailed from Sanlúcar de Barrameda in 1535. He reached the estuary of the Río de la Plata in January and founded Buenos Aires in 1536. Attacks by the indigenous people, scarcity of food, and various disasters made the site untenable. Leaving Juan de Ayolas in charge, Mendoza sailed for Spain in 1537 and died at sea. Buenos Aires was abandoned in 1541, by order of Domingo Martínez de Irala, and the colonists moved to Asunción.
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