Machu Picchu, the most famous landmark of Inca civilization, was believed to be built around A.D. 1438. A new study, co-authored by Jason Nesbitt, associate professor of anthropology at the School of Liberal Arts, suggests the citadel may have been built some two decades earlier. Nesbitt, along with researchers from Yale and the University of California–Santa Cruz used accelerator mass spectrometry (AMS) — an advanced form of radiocarbon dating — to determine the age of human remains recovered during the early 20th century at the site.