The roads of the Inca

How an empire without wheels or horses held itself together

At the height of its power, in the early sixteenth century, the Inca empire stretched for some four thousand kilometres along the spine of the Andes, from what is now southern Colombia to central Chile. Its rulers had no horses, no wheeled vehicles and no iron tools, and they governed a land of deserts, forests and mountains that rise above six thousand metres. What held it together was a network of roads known as the Qhapaq Ñan, or 'royal road', which ran out from the capital, Cusco, towards each of the four quarters into which the empire was divided. With all its branches, the network extended for more than 30,000 kilometres. It remains one of the great engineering achievements of the pre-industrial world.

There were two main highways. One ran along the Pacific coast, through the coastal deserts; the other followed the highlands, crossing passes more than 4,000 metres above sea level. Many shorter roads linked the two and led down to the forests of the east. The Incas did not build all of this from nothing. A good deal of it consisted of older tracks and roads laid down centuries earlier by peoples such as the Wari, which the Incas repaired, widened and joined up into a single system.

The labour came from the people themselves. The Incas had no money, and in place of taxes each household owed the state a period of work, a system known as the mit'a. Some men were sent to the army or to state farms, and others were put to work on roads. Each community was responsible for the stretch that passed through its own territory, and it was kept in good order. Where a road climbed steep ground, the builders cut stone steps into the hillside, supported the edge with retaining walls and dug channels to carry away rainwater, which would otherwise have washed the surface away. On level ground the road was often paved and wide enough for several people to walk side by side; in the mountains it narrowed to little more than a footpath.

Rivers and gorges were crossed by suspension bridges. Cables were twisted from the tough grass of the high plateau, stretched across the gap and anchored to stone pillars on each side. Bridges of this kind rot quickly, so they had to be renewed regularly, and the tradition has survived. Every June, families from villages near Huinchiri, in southern Peru, still weave a new bridge over a gorge on the Apurímac river and discard the old one. Spanish chroniclers wrote with wonder about such bridges, amazed that something so slight could carry loaded men and animals.

Travellers on official business were looked after along the way. Rest houses called tambos stood roughly a day's walk apart, offering shelter and food, and beside many of them were storehouses filled with maize, dried potatoes, cloth and weapons. An army could therefore march for hundreds of kilometres without carrying its own supplies, and the state could provision its soldiers wherever they were needed.

The roads also carried information. Teams of trained runners, known as chasquis, were stationed in small huts a few kilometres apart. A runner would sprint along his stretch and hand the message to the next man, who was already waiting to take it on, and the blast of a conch-shell trumpet warned the next station of his arrival. Most messages were spoken, but they were often accompanied by a quipu, a bundle of knotted cords used to keep records. By this relay system a message could cover well over a hundred kilometres in a day, far faster than any army could march.

The roads were not open to everyone. They belonged to the state, and ordinary people did not use them for journeys of their own without permission. The traffic consisted of officials, soldiers, messengers and the llama caravans that carried goods. A llama can bear only about 25 kilograms and, unlike a horse, cannot carry a rider, so that although news travelled fast, goods moved slowly. The roads were also used to move people: when the Incas conquered a region, they sometimes resettled whole communities there in order to make it more secure.

When the Spanish arrived in 1532 under Francisco Pizarro, the roads that had bound the empire together helped to bring it down, for they allowed the invaders to move quickly through the mountains. Once the Inca state had collapsed, the labour system that kept the roads in repair disappeared with it. Bridges, which needed constant renewal, soon fell, and many sections were abandoned or built over. Yet much has survived. Villagers still use long stretches as footpaths, and the best known section, the Inca Trail to Machu Picchu, is walked by many thousands of visitors every year, although the number allowed each day is now limited. In 2014 UNESCO added the Qhapaq Ñan, which crosses six countries, to its World Heritage List.