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.