The royal family formed an educated, governing upper nobility, which at the time of the Spanish conquest numbered around 500. To further increase government control over an empire grown unwieldy, all who spoke Quechua became an "Inca class" by privilege and became colonists. Lesser administrative officials, formerly independent rulers, and their descendants were the minor nobility, or curaca class, also supported by the government.

For purposes of administration the empire was divided into four parts, the lines of which met at Cuzco; the quarters were divided into provinces, usually on the basis of former independent divisions. These in turn were customarily split into an upper and a lower moiety; the moieties were subdivided into ayllus, or local communities. Much as it exists today as the basic unit of communal indigenous society, so the ancient ayllu was the political and social foundation of Inca government. When a territory was conquered, surveys, consisting of relief models of topographical and population features, and a census of the population were made. With these reports, recorded on quipus, of the material and human resources in each province, populations were reshuffled as needed. Thus transplanted, and dominated by Quechua colonists, the subject peoples had less chance to revolt, and the separate languages and cultures were molded to the Inca pattern.

Religion, controlled by a hierarchy similar to the government hierarchy, emphasized ritual and organization. Heading the Inca gods was Viracocha. His servants were the sun, the god of the weather or thunder, the moon, the stars, the earth, and the sea. The sun god was foremost among these. Divination, sacrifices (human only at times of crisis), celebrations and ceremonies, ritual, feasts, and fasts were all part of Inca religion.

Although the Andean area offered a diversity of plant domestication, the handicaps of terrain and climate presented severe obstacles. To overcome them, Inca engineers demonstrated extraordinary skill in terracing, drainage, irrigation, and the use of fertilizers. They lacked draft animals, but domesticated animals (the llama, the alpaca, the dog, the guinea pig, and the duck) were important to daily living; from the wild vicuña, fine wool was sheared.

Without paper or a system of writing, the architects and master masons who designed and supervised the construction of public buildings and engineering works in such cities as Machu Picchu and the fortress of Sacsahuamán built clay models and, in actual construction, employed sliding scales, plumb bobs, and bronze and stone tools. Without wheeled vehicles for transport, the huge polygonal stone blocks for fortress, palace, temple, and storehouse were emplaced by ramp and rollers and were fitted with extraordinary precision. Wall corners were always carefully bonded. Adobe bricks and plaster were common, especially along the coastal desert. Buildings were usually of one story.

One of the most remarkable evidences of Inca engineering skill was an elaborate network of roads, which in many places still survives. Streams were crossed by a log or stone bridge, placid rivers by balsa ferry or pontoon bridge, and chasms by a breeches-buoy contrivance or by a suspension bridge that might be as much as 200 ft (60 m) long. Road sections were maintained by the nearest village, as were the shelters and military storehouses that were spaced a day's travel apart; a village also supplied messengers for its sector. These men, serving 15-day shifts, relayed messages about every mile. About 150 mi (240 km) could be covered daily, a distance that later took the Spanish colonial post 12 to 13 days to cover.

In the manufacture of textiles the Inca utilized almost every available kind of fiber and produced elaborate multicolored tapestries. In ceramics they achieved a fine-grained, highly polished, metallic hardness that stressed functional and utilitarian design. Mining was fairly extensive. Of the metals, copper and bronze were for public use; gold, silver, and tin were reserved for the emperor, the temples, and the upper nobility. Metallurgical processes included the techniques of smelting, alloying, casting, hammering, repoussé, incrustation, inlay, soldering, riveting, and cloisonné.

See chapters on the Inca in the Handbook of South American Indians, Vol. II (1963). For accounts by early historians, see P. de Cieza de Léon, The Incas (tr. 1959) and G. de la Vega, The Royal Commentaries of Peru (tr. 1966).

See also W. H. Prescott, The History of the Conquest of Peru (1855, repr. 1963); C. R. Markham, The Incas of Peru (1910, repr. 1969); P. A. Means, Ancient Civilizations of the Andes (1931, repr. 1964) and The Fall of the Inca Empire (1932, repr. 1964); H. Bingham, Machu Picchu: Lost City of the Incas (1948, repr. 1969); V. W. von Hagen, Highway of the Sun (1956); L. Baudin, A Socialist Empire: The Incas of Peru (tr. 1961) and Daily Life in Peru under the Last Incas (tr. 1962); J. A. Mason, The Ancient Civilizations of Peru (rev. ed. 1968) and A. Métraux, The History of the Incas (tr. 1970); G. W. Conrad and A. A. Demarest, Religion and Empire; The Dynamics of Aztec and Inca Expansionism (1984).