Transporting timbers to Chaco Canyon: How heavy, how many carriers and how far/fast?
A total of 200,000+ large timbers were transported >75 km to Chaco Canyon, a political and religious center in the precontact U.S. Southwest, using only human power. Previous researchers reported that typical primary roof beams (vigas) of Chacoan Great Houses averaged 0.22 m in diameter and 5 m in length with a mass of 275 kg. However, the 275 kg mass appears to be a miscalculation. Here, we calculate that a ponderosa pine timber of the stated dimensions would have a mass between 85–140 kg depending on the water content. While still a prodigious load, this recalculated mass requires revisions to estimates of the labor, time, and energy required to build Great Houses at Chaco. Based on contemporary measurements on professional load carriers and soldiers, we estimate that as few as two people could have carried an 85 kg timber across 100 km in as few as 21 h of active walking.