One of the largest demographic shifts to occur in Andean prehistory took place during the Late Intermediate Period (A.D. 1000–1400). Across a large expanse of the central Andes a vast number of lower elevation settlements were abandoned and local populations were concentrated in newly constructed, defensibly positioned sites, located along high ridges. In this article we examine this dramatic settlement shift in relation to the Chanka ethnic group that occupied the Andahuaylas region (Department of Apurimac, Peru). The results indicate that the shift from valley to hilltop settlements in the Andahuaylas region occurred around A.D. 1000. We propose that the shift reflects an increased dependency on agro-pastoralism that resulted from a period of climate change. We also suggest that in this region of the Andes the shift was augmented by growing levels of political competition after the dissolution of the Wari Empire and that current models, which situate the Chanka as a uniquely powerful ethnic group at the time of the Inca expansion, need to be reexamined.