Just when Mexico celebrates the foundation of Tenochtitlan, capital of the Mexican empire located in present-day Mexico City, another new scandal shakes the world of antiquities. 

The discovery of up to a dozen documents written by the colonizer Hernán Cortés that had been auctioned by several well-known houses and that were fraudulently stolen from the National Archive of Mexico (AGN), taking advantage of the chaos of the institution's records.

It all started last September with a conspiratorial letter. 

The Swann Galleries auction house in New York put up for sale this five-year-old missive that revealed a political intrigue in which Cortés was involved.

The document was about to go on the market for up to $30,000 when a group of seasoned researchers from Spain and Mexico surprisingly thwarted the auction. 

Diving into auction house catalogs and making use of a team member's photographic archive of colonial documents, the scholars discovered that the letter signed in 1521 came from the ANG and that there were as many as nine other Cortés documents that had been sold in recent years by prestigious auction houses and belonged to the same archive.

This was confirmed to Reuters by officials of the Mexican institution, who added that some of these documents were previously bound in old books and were stealthily and carefully extracted from them. 

María Isabel Grañén, a scholar of 16th century Spanish colonial books and a researcher on the team, called the discovery a "scandal." "We are very concerned, not only about this theft but about all the theft and looting that exists of cultural heritage," she said. 

Given the obscurantism of the auction sector, the names of the buyers never came to light. The houses involved were quick to deny responsibility and claimed that they carefully examine all items prior to their sale. 

However, Swann Galleries canceled the auction of Cortes' plotting house and the outcome of the inquiries has forced the Mexican police and the U.S. National Bureau of Investigation (HSI) to open an investigation. 

According to Reuters, the Mexican Ministry of Foreign Affairs has requested the cooperation of the U.S. Department of Justice to repatriate the 10 missing manuscripts to the Mexican archive. 

Mexico has been fighting for years against the plundering of its historical heritage and for the repatriation of relics displayed in foreign museums and private collections. 

The scandal of the Cortés documents joins other allegedly fraudulent auctions such as the one that took place barely four months ago in Paris, where Christie's put up for sale stolen pre-Hispanic pieces, some of them fakes. 

The problem is complex to say the least, because once the pieces of questionable provenance are auctioned, they become legally owned and there is no way to return them to the country from which they were stolen. 

In the case of the United States, this type of crime is easier to detect because the legislation requires the provenance of the auctioned objects to be certified and because, once the responsible parties are brought to trial, it is the plaintiff who proves the ownership of the pieces. 

However, in other countries, such as France, there are no bilateral agreements in this sense, which facilitates looting. 

"Auctions are the mechanism for laundering these goods," said the director of Mexico's National Institute of Anthropology and History (INAH), Diego Prieto Hernandez, when the provenance of the 27 Aztec pieces auctioned at Christie's in February came to light. 

Prieto also explained that in cases like the one in France, even Interpol's hands are tied. 

The Hernán Cortés manuscripts do not seem likely to follow a similar fate.

Collectors such as the Brazilian art historian, Pedro Correa do Lago, returned a letter of Cortes that he bought from Swann Gallery a few years ago after learning of its provenance.

Mexico has also announced that it will sue the auction houses involved in the sale of these documents, which are, in fact, quite unique in the art market. 

The question now is how to stop the indiscriminate theft of a country's cultural and historical heritage and how much more of it will continue to happen.