Vilca (Anadenanthera colubrina) is a small leguminous tree occurring as a species component of the dry tropical forest of the Urubamba and other Andean valleys. The powerful psychotropic properties of its seeds account for the long and important place of this plant in Andean culture history. Archaeological evidence from painted pots, snuff tubes, bone pipes and clyster tubes indicate its diverse modes of past use. Wari and Inca artifacts, as well as the reconstruction of Inca history from early colonial documents, suggest the role of vilca in shamanic-style religion and medicine. When understood that the tryptomines in vilca trigger a characteristic three-stage hallucinogenic experience, new interpretations emerge of several aspects of the Andean past. Vilca uses can be implicated as a feature of oracle shrines at pre-Columbian religious sites as well as the behavior of the Chanka people, enemies of the Incas. After the Conquest, vilca was the substance behind the drug-induced manifestations of the so-called Taqui Onccoy movement. Strong Spanish opposition to vilca which was viewed as a diabolical intervention of Satan, had much to do with the competition it was perceived to pose to Catholic conversion.