Sacsayhuamán

For most of a year in 1536 and 1537, the hill above Cusco was the most dangerous place in South America. Manco Inca, who had been installed by the Spanish as a compliant ruler and had stopped being one, brought an army down on the city and his forces took Sacsayhuamán. From the top of the terraces they could see every roof in Cusco, and they set most of them alight. Slingers worked from behind the wall's teeth, which give a defender an angle on anyone approaching the face of the next section along.

The Spanish counterattack was led by Juan Pizarro, brother of Francisco. He took a blow to the head during the assault and died of it within days. The hill fell anyway. Chroniclers report that the last Inca commander holding the tower threw himself from the top rather than be taken. Of the three towers that stood up there, only the foundations survive; one was circular, and water was piped into it.

What It Took To Build

Construction began in the mid-fifteenth century under Pachacuti, the ruler who turned the Inca state into an empire, and continued under his successors. It was still not finished when the Spanish arrived. The chronicler Cieza de León reports twenty thousand people working in rotation, drafted province by province under the labour tax that funded everything the Inca built. The number is a chronicler's estimate, but the scale is not in doubt.

Most of the giant blocks are limestone from quarries nearby. Moving them meant rope, log rollers, earth ramps and very large numbers of people. There was no wheel here and no draught animal; the llama carries a sack and refuses anything heavier. The largest stones in the lowest course are generally estimated at well over a hundred tonnes.

The harder problem was the joints. The blocks are not rectangular. Each one is cut with many faces, to match the specific stones it will sit against, with no mortar anywhere. That means the final shape of a stone can only be decided once its neighbours are in place; every block in the wall belongs to exactly one position in it. The wall also leans slightly inward and the corners are rounded, which is not decoration. This is earthquake country, and that geometry lets the stones settle back into each other when the ground moves.

The Part That Could Be Carried Away

After the conquest, Sacsayhuamán became a quarry. Colonial Cusco needed cut stone for churches, monasteries and mansions, and there was no sense hauling it from a distance when a mountain of perfectly dressed masonry sat on the hill above the city. The towers came down. The upper courses came down. A great deal of what you now see in the foundations of colonial Cusco started up here.

What could not be moved was the bottom course. No cart would take those blocks and nothing available could pull the cart. The famous zigzag wall survives because it defeated the people dismantling it.

The Test

In 1950 a major earthquake hit Cusco. Colonial churches and houses cracked open, and some came down entirely. The Inca walls, unmaintained for four centuries, did not shift. Walk the old streets today and you can read the two layers stacked on each other: mortarless Inca stonework below, later masonry above it, repaired more than once.

One more thing worth knowing. It is often said that Cusco was laid out in the shape of a puma, with Sacsayhuamán as the head and the zigzag wall as its teeth. The reading comes from colonial-era sources and is disputed among scholars. It is also very hard to unsee once someone has told you.

Now

The site has been inscribed with the historic centre of Cusco on the UNESCO list since 1983 and is run as an archaeological park. Every June the Inti Raymi festival is staged on the flat ground below the walls, a tradition revived in the 1940s and now watched by tens of thousands.

The threats are slow ones: rain cutting into the terraces, several hundred thousand pairs of feet a year wearing the turf and soil, dry-season grass fires on the slope, and Cusco itself climbing the hill. The wall has been in the same place for five hundred years. Who built it, who defended it, who took it apart and who protects it has changed every century since.