In former years, an archaeological field school offered through Harvard's Summer School Program, conducted in the residential area outside the monumental core, has provoked controversy amongst local archaeologists. The program was directed by Dr. Gary Urton, of Harvard, who was an expert on quipus, and Dr. Alexei Vranich of the University of Pennsylvania. The controversy was over allowing a team of untrained students to work on the site, even under professional supervision. It was so important that only certified professional archaeologists with documented funding were allowed access. The controversy was charged with nationalistic and political undertones. The Harvard field school lasted for three years, beginning in 2004 and ending in 2007. The project was not renewed in subsequent years, nor was permission sought to do so.