Amateur sleuths traced stolen Cortés papers to U.S. auctions. Mexico wants them back

FILE PHOTO: A Hernan Cortes letter, signed "El Marques", to his mines administrator Pedro de Castilleja is seen in Mexico City, Mexico July 20, 2010. Archivo General de la Nacion AGN/Courtesy of Maria del Carmen Martinez/Handout via REUTERS

MEXICO CITY (Reuters) - In September, a New York auction house had a rare treasure up for sale: a five-centuries-old letter revealing political intrigue involving Hernán Cortés, the famed leader of the Spanish force that colonized what is modern-day Mexico.

Cortés papers seldom come to market. The 1521 document, offered by Swann Galleries, was expected to fetch $20,000 to $30,000. That is, until a plucky group of academics in Mexico and Spain helped thwart the sale.