The latest report released by Peruvian authorities uncovered that Yale University is holding over 40,000 artifacts from the Inca citadel of Machu Pichu, roughly ten times the number of pieces that has been initially reported by the university.

In an telephone interview, Yale Archaeology professor Richard Burger said, as quoted by Yale Daily News: “Counting is complicated,” he said. “Do you count lots or do you count every piece? There may be tens of thousands of objects if you count each finger bone in a skeleton.”

Burger was responsible for creating the inventory of the Inca pieces months ago. Last year, the Peruvian government and Yale University reached an agreement which stated that the university will return 4,000 pieces that were taken from the Inca temple one century ago.

The unexpected outcome of a second inventory of the pieces brought to light ten times more items than previously counted, as announced by Health Minister Hernan Garrido Lecca, lead negotiator with Yale.

In the end, it is all a matter of the criteria used when making an inventory, Burger said, more precisely which pieces to classify as museum-quality and which to classify as non-museum quality.

Yale explorer Hiram Bingham III started excavating the artifacts in 1911, and in an agreement with Peru’s government, he brought the artifacts to Yale as a loan. The pieces of inestimable value were supposed to return to Peru 18 months later, but that never happened.

In 2006, Peruvian officials threatened with a lawsuit, unless the artifacts were returned. Yale’s attempts to arrange a split of the collection failed, and one year later the two parts agreed to an international traveling exhibition of the artifacts, which would later end up in a special museum co-sponsored by Yale.

Museums famous for their exhibitions are currently facing challenges such as this, as countries all over the world, like Egypt, Peru or Greece, are trying to regain artifacts that are rightfully theirs, but have been taken out of the countries by various explorers.