Nothing much has happened in this valley since. Six pyramids, also called platform mounds, are arranged around a huge public plaza area and dominate the archaeological site. Researchers believe all of the central pyramids were built in only one or two phases, indicating the presence of complex planning, centralized decision-making and mobilization of large labor forces. Excavations at the Piramide Mayor revealed a terraced pyramid, with staircases leading up to an atrium-like platform. The final ascent leads to the flattened pinnacle, consisting of a group of rooms and a fire pit that was heavily used, probably for ceremonial or religious activities.
Researchers also have surmised construction methods.
Dr. Creamer said the ancient Peruvians used shicra, or reeds, to weave mesh bags. They filled the bags with rocks from the nearby riverbed and hauled them to the construction sites. In her excavations, Ruth Shady has actually been able to retrieve the rocks from individual bags. The research team took samples of the mesh bags for radiocarbon dating. The annual plants that grew and died in a year make the best carbon samples because they give you the most reliable dates.