Sierra de la Plata

The Sierra de la Plata was a mythical source of silver in the interior of South America. The legend began in the early 16th century when castaways from the Juan Díaz de Solís expedition heard indigenous stories of a mountain of silver in an inland region ruled by the so-called White King. The first European to lead an expedition in search of it was the castaway Aleixo Garcia, who crossed nearly the entire continent to reach the Andean altiplano. On his way back to the coast, Garcia died in an ambush by indigenous tribespeople in Paraguay, but survivors brought precious metals back to corroborate their story.

The legend inspired other expeditions, all of which ended in failure. However, numerous expeditions allowed Spanish Conquistadors deeply explored the South America south of Brazil. The outposts founded during the expeditions gradually evolved into Buenos Aires and Asunción, the lands colonized by the Spanish became Viceroyalty of the Río de la Plata.

Wikipedia