Tawantinsuyu, the four parts together, was assembled in under a century. Terence D'Altroy's account describes an expansion from the Cusco valley in the early fifteenth century to a state running four thousand kilometres along the Andes, held together by a road system, storehouses, resettled populations and a labour tax paid in work rather than in goods.
Religion was one instrument of that expansion. Conquered peoples kept their own huacas, but their principal images were brought to Cusco where they served in effect as hostages, and the sun cult and the Inca calendar were imposed above them. The state also took women, the aqllakuna, into enclosed houses to weave and to brew for the cult.
The Spanish arrived in 1532 during a war of succession between Atahualpa and Huascar, seized Atahualpa at Cajamarca and executed him the following year. Everything written about Inca religion was therefore written after the collapse, by or for the victors. The partial exceptions are Garcilaso de la Vega, son of a conquistador and an Inca noblewoman, who wrote from Spain half a century later, and Juan de Betanzos, who married into the Inca elite and is the closest thing to an insider account. The atlas treats all of them as testimony requiring the same scrutiny.