Since prehistoric times Andean societies have been organized around the ayllu a grouping of real or ceremonial kinspeople who share labor resources and ritual obligations Many Andean scholars believe that the ayllu is as ancient as Andean culture itself possibly dating back as far as 6000 B C and that it arose to alleviate the hardships of farming in the mountainous Andean environment In this boldly revisionist book however William Isbell persuasively argues that the ayllu developed during the latter half of the Early Intermediate Period around A D 200 as a means of resistance to the process of state formation Drawing on archaeological evidence as well as records of Inca life taken from the chroniclers Isbell asserts that prehistoric ayllus were organized around the veneration of deceased ancestors whose mummified bodies were housed in open sepulchers or challups where they could be visited by descendants seeking approval and favors By charting the temporal and spatial distribution of chullpa ruins Isbell offers a convincing new explanation of where when and why the ayllu developed