Machu Picchu: Why the Inca Built a City That Nobody Could Reach

Machu Picchu sits at 2,430 metres above sea level in the Peruvian Andes, surrounded on three sides by near-vertical mountain drops and accessible, until the 20th century, only by a narrow mountain path that takes several days to walk. Building anything here would be a serious engineering challenge today. Building a city of 200 structures here in the 15th century, without iron tools, without wheeled vehicles, and without mortar, is one of the most remarkable feats in human history.

The city was built around 1450 AD, probably as a royal estate for the Inca emperor Pachacuti. It was occupied for fewer than 100 years before being abandoned — likely during the Spanish conquest — and then remained unknown to the outside world until 1911, when American explorer Hiram Bingham was guided to it by local farmers who had known about it all along.

Building Without Mortar — and Why It Works Better

The most immediately striking thing about Machu Picchu's construction is that none of the stones are held together with mortar. They are simply cut and fitted together with extraordinary precision — a technique called ashlar masonry. The joints between stones are so tight that in the finest examples, a piece of paper cannot be slid between them.

This is not a primitive technique. It is a sophisticated engineering choice. In an earthquake-prone mountain environment, mortar-based construction is actually inferior. When the ground shakes, rigid mortar joints crack and the structure fails. Dry stone walls, by contrast, flex slightly — the stones shift fractionally against each other and then settle back into position. Machu Picchu has survived numerous significant earthquakes over 600 years with minimal structural damage. Spanish colonial buildings constructed with mortar in the same region have repeatedly been destroyed.

"The Inca did not use mortar because they lacked the knowledge to make it. They chose not to use it because they had developed something better — a construction system perfectly adapted to the seismic environment they inhabited."

How They Shaped the Stones

The Inca had no iron tools. Their stone-working was done with harder stones — primarily quartzite hammers — used to peck and grind granite into shape. This is extraordinarily labour-intensive. A single large stone might require months of work by multiple craftsmen.

The genius of the Inca system was in the workflow. Stones were roughed out at the quarry to reduce their weight before transportation. They were then moved to the building site — sometimes kilometres away, down and up mountain slopes — using a combination of wooden sledges, earthen ramps, and human labour organised in large teams using rope systems and levers. The final precision fitting was done in place, with craftsmen grinding and testing the surfaces repeatedly until the fit was perfect.

The Drainage System That Saved the City

Building at altitude in the tropics means dealing with extraordinary rainfall. The Andes receive intense precipitation that, on steep mountain terrain, rapidly becomes destructive runoff capable of destabilising foundations and triggering landslides. The Inca solved this with a drainage system of remarkable sophistication.

Approximately 60% of Machu Picchu's construction is below ground — a hidden infrastructure of crushed white granite layered over clay, creating a drainage substrate that channels water away from foundations at a controlled rate. The city sits on this engineered base rather than directly on the mountain. Combined with surface drainage channels cut into the paths and plazas, the system prevents waterlogging and erosion with a reliability that has kept the structures stable for six centuries.

Why It Was Abandoned

Machu Picchu was abandoned around 1572, several decades after the Spanish conquest of the Inca Empire began in 1532. The most likely explanation is a combination of factors: the smallpox epidemic that preceded the Spanish, which killed large portions of the population including the emperor Huayna Capac; the civil war that followed; and the disruption of the Inca administrative system that would have supplied and maintained a remote royal estate.

The Spanish conquistadors never found Machu Picchu. Its remote location, which made it so difficult to build, also protected it from destruction. The city that took the most extraordinary effort to create was saved, ultimately, by being too hard to reach.