How Many People Lived in the Chaco Regional System, and Why It Matters

Using a new approach to estimating its population assuming an Ideal Free Distribution, we suggest that even the highest estimates for the population served by the Chaco Regional System at its height have been somewhat too low. This complements recent findings that the US Southwest was greener and more productive for the millennium prior to about AD 1200 than afterwards, and that crude birth rates in this region, particularly in the San Juan Basin and northern San Juan regions, were high on both regional and worldwide scales from the last half of the first millennium into the early second millennium AD. We raise the possibility that the striking expansion of the Chacoan Regional System ca. A.D. 1040 should be understood through the lens of colonial systems, and demonstrate that developments in collective computation such as Chaco’s roads and shrines/signaling stations are to be expected in polities of Chaco’s scale.