Machu Picchu

A royal estate, not a fortress

Machu Picchu was not, as Hiram Bingham believed when he announced its discovery in 1911, a "lost city" or a "fortress of the Incas".

It was a royal estate, built in the mid-fifteenth century for the Inca emperor Pachacuti Yupanqui (who reigned 1438–1471) on a high saddle ridge between two peaks at 2 430 metres in the Vilcabamba range of the Peruvian Andes.

The site held about 750 people at its peak, mostly servants and attendants of the royal household. The Incas used it for perhaps a hundred years and then abandoned it sometime in the early sixteenth century, before the Spanish conquest of 1532. The Spanish never found it, which is the reason it survived intact.

Stones fitted without mortar

The defining feature of Inca masonry — visible at Machu Picchu in its most refined form — is dry-stone polygonal fitting.

Each block of grey andesite has its mating faces ground down to match the contours of the block beneath, so precisely that no mortar is needed and a knife blade cannot be inserted between blocks. Some blocks have a dozen or more faces, each one fitted to a different adjacent stone.

The technique was developed without iron tools. The Incas had bronze, but not steel — using only harder hematite hammerstones and dry sand abrasive. Laser measurements show the joints at the Temple of the Sun are typically less than one millimetre.

Engineering at altitude

The site is built on a steep ridge that should not, by ordinary engineering, support a settlement of any size.

The Inca solution was a multi-layered earthworks system. Terraces of dry-stone retaining walls 4 metres deep were filled with successive layers of large stones (for drainage), then smaller stones, then sand, then topsoil hauled up from the valley. The terraces stabilised the slope against landslides and provided agricultural land for maize and quinoa.

A sophisticated water supply ran from a natural spring through 16 stone-lined fountains that descend the city in a stepped sequence, providing fresh water to every quarter without pumps.

Lost because no one cared

The story that Machu Picchu was "lost" is a Western convention.

Local Quechua farmers had been cultivating its terraces for generations when Hiram Bingham, a Yale-affiliated explorer and later US senator, arrived in July 1911. Bingham hired the 11-year-old son of a local farmer, Pablito Alvarez, to lead him to the ruins. The ruins were partly cleared of vegetation already because Quechua farmers used them.

Bingham's contribution was to photograph the site systematically, publish it in National Geographic in 1913, and remove approximately 5 000 artefacts to Yale's Peabody Museum. Most of which were finally repatriated to Peru only in 2012, after a hundred years of dispute.