The Incas inherited an unforgiving geographic landscape. Despite its overwhelming beauty, its various terrains held hazards and risks. The Four Quarters of the Inca kingdom stretched along a narrow band of Pacific Ocean frontage extending from Chile up to Columbia, 2500 miles long, and ranging inland from the dry coastal desert to a fingerhold on Amazonian jungle. Elevations went from sea level to 22,000 feet, and while the highest zones were not regularly lived in, some housed ceremonial structures, and many of the people lived quite well at altitudes of 15,000 feet. Deep ravines scour the jagged mountains and the flat plains, home to at-times torrential rivers and streams, making travel even more difficult.

Yet is is known that the people of the Inca were able to traverse their land from end to end, and from shore to highest regions, on a regular basis. The economy and the security and the governance of the kingdom depended on it. The Inca, for all that they never used the wheel, were engineers of the first rank, drawing on the knowledge gained from the societies that preceded them, and bringing this technology up to the next level.

The inhabitants lacked wheeled conveyances, possibly because they lacked any draft animals strong enough to pull heavily-laden carts (although your author has seen contemporary llamas hitched to wheeled carts in which men sat, fully capable of moving them efficiently). However, wheels would be a liability in the mostly up-and-down terrain in which both people and pack animals had to operate. People beyond the age childhood cannot ride llamas, so the latter were employed as pack animals. Their sure-footedness in the Andes was entirely an asset. People walked, or if wealthy, were transported on conveyances carried between poles by servants.

The Incas under Pachacuti developed a lengthy system of roads. By the shore, these roads were nothing more than paths marked by tree trunks, although the coastal road extended nearly the entire length of the empire. Highland roads were sturdy and built to last down the centuries. Flat stones were laid, and sometimes walls were constructed for safety on the edges of peaks and ravines. Without hard metal, rock in the way might be hewn through. The road system of the Incas measured about 22 thousand miles (although another source gives a figure of 14 thousand), around half of it paved. Some roadways were narrow, but others, apparently mostly used for troop movements or ceremonial processions, were up to 15 feet wide.

Bridges were built across ravines. Some of these were close to the stream that may have rushed underneath, others were incredible feats of derring-do to cross, not to mention build in the first place. The smaller streams usually were forded with bridges made of stone, but larger crossings required suspended rope or braided withe bridges. At times, these would be anchored to stone on the banks, or, with those closer to the water they crossed, slightly elevated causeways would serve as the approach. Three or four long cables of braided grasses would form the floor of the bridge, and provide the structural strength. Across them, for footing, would be laid sticks or cane. Usually, two more cables served as guard or hand rails. Vines or rawhide thongs would be used to fasten everything together. They were very sturdy, although on a windy day one would not be apt to think so! The bridges would sag and sway in the wind. One of the more dramatic examples of such a bridge is that which crosses the river Apurimac, a river which eventually flows into the Amazon. It stretches 220 feet across the ravine, at a height of 118 feet. Repairs on these bridges had to be frequent, and they could easily be dismantled at the approach of an enemy.

There were approximately 2,000 tampos (rest houses) placed at even intervals along the trails. Larger ones were placed about a day's journey apart from each other, and even larger ones were meant to provision large troop movements. The tampos provided food and shelter, plus corrals for pack llamas. Stored provisions included such items as such as corn, lima beans, dried potatoes, and llama jerky. Where climate permitted, local villagers planted fruit trees along the roads for use by travellers. While the common folk had to obtain permission to use the roads, there was still plenty of traffic what with chasqui runners, military, and food / supply movements. Chasqui runners were the bearers of the quipu, or simply carried memorized messages, and could pass information from Qosqo to the ends of the kingdom within about a week, by using a relay system which would keep the runners fresh.

These roads are so well built that they are in many places still in use today.

....

The common folk lived in one-room dwellings, typically with just a door and no windows. After all, home was mostly just a place to sleep out of the weather. Homes often joined one another in a connected row of houses. Homes were typically of local stone, with thatched roofs. Doors, and windows when present, tended to be trapezoidal in shape, which added to the stability of the structure. Thatched roofs were less likely to cause damage during earthquakes. Corners on buildings and walls were likely to be rounded, another good construction practice in seismically-unstable terrain.

One of the most outstanding examples of Inca building technique is the "fortress" of Sacsahuaman, near Qosqo. Built of irregular blocks of limestone rock, it was initially believed to be a military structure, but more recent investigations have concluded that the place was constructed more for ceremony and probably for astronomical observations. The three defensive walls may have been added later. Access within was gained via lintel-topped gates. The Inca had mastered the art of structural stability without the use of mortar, or the use of tools of iron (iron being rare in the region).

The massive stones fit together meticulously, despite the various sizes and shapes. All the sources the author has read make note that the stones are so tightly placed with each other that it is impossible to insert a knife blade between them, and thus this author follows suit. Walls are angled leaning back into the soil behind them; a smart move on the part of the builders, (and one that the builder of the much more recent stone wall on the author's property would have done well to have heeded). To break stone into shape, the Inca made use of natural fissures and implements of stone, copper or bronze, and might grind neighboring rocks against each other to wear them down for proper fit. Without any wheels, levers and temporary construction ramps would have been essential, along with massive manpower and a strictly-organized society.

Geography of the Inca Empire
Inca Civilization
Ephraim George Squier, 1877. Peru: Incidents of Travel and Exploration in the Land of the Incas.
Carmen Bernand, 1988. The Incas: People of the Sun.ISBN 0-8109-2894-9.
The Inca and Their Roads
Wikipedia: Inca Road System
Inca Roads and Bridges
Wikipedia: Inca Rope Bridges
NOVA Online Adventure (Lost Empire)
Jeff L. Brown, Water Supply and Drainage at Machu Picchu
Wikipedia: Inca Architecture
Maria Longhena and Walter Alva, 1999. The Incas and other Andean Civilizations. Thunderbay Press. ISBN 1-57145-220-6

Inca Trail: Pajaro
Sacsahuaman: Wikipedia (uncredited)