Sacsayhuamán & Machu Picchu

Two sites, one valley

Sacsayhuamán sits on the hill above Cusco. Machu Picchu is eighty kilometres north-west, on a ridge between two peaks above the Urubamba. Both are Inca, both are fifteenth century, and they raise completely different questions.

Sacsayhuamán: the wall

Three tiers of zigzag walls, several hundred metres long. The largest blocks in the lowest tier are estimated at over a hundred tonnes, and some figures go considerably higher. They are limestone and diorite, cut with irregular polygonal faces, and fitted so closely that the joints are often described as bladeless.

What makes the masonry remarkable is not the size alone. It is that the blocks are not rectangular. Each one has a unique shape with many faces, and every face meets its neighbours precisely, including on surfaces buried inside the wall where nobody would ever see them.

The quarries are known. The ramps are known. The method is still argued over.

Quarry sites have been identified at Rumiqolqa and elsewhere, along with abandoned blocks in transit and the remains of hauling ramps. So the stones were moved by people, from identifiable places, over ground that has been surveyed. That part is not mysterious.

How the faces were shaped to fit is the open part. Proposals include repeated lowering and scribing, pounding with harder hammerstones, and the use of sand abrasion. Experimental archaeology has reproduced the technique at small scale. Whether it scales to the hundred-tonne blocks at the rate the Inca worked is where reasonable people still disagree.

Machu Picchu: the ridge

Built around 1450, most likely as a royal estate for the ruler Pachacuti, and occupied for roughly a century before it was abandoned around the time of the Spanish conquest. It was never found by the Spanish, which is why it survived.

The engineering that impresses professionals is not the walls but the drainage. The site sits on a steep slope in a region that gets serious rainfall, and it has held together for five centuries because a large proportion of the construction is underground: terraces layered with stone chips, gravel and soil, with a designed drainage system beneath. Some estimates put well over half the total construction effort below the visible surface.

The sky here

At 13.2° S, the sun passes directly overhead twice a year, and the solstice sunrise swing is narrow. The Intihuatana stone at Machu Picchu and the Torreón window are both argued to mark solstice positions, and the June solstice alignment through the Torreón is reasonably well documented.

The Inca also read the sky differently from European traditions: alongside star constellations they identified dark cloud constellations, shapes in the dark bands of the Milky Way rather than in the stars themselves. The llama, the fox, the toad. That is worth sitting with. Two cultures looking at the same sky and one of them organising it by the darkness.

What is still open

On Ancient Apocalypse

Peru features in the second season of the Netflix series, which focused on the Americas. The claim in play is that the finest megalithic work predates the Inca and descends from an earlier lost culture. The archaeological counter-position is that Inca stoneworking developed over generations, is visible in intermediate stages at multiple sites, and is dated by the same methods used everywhere else.

Worth knowing for context: for the second season, filming permits at Grand Canyon and Chaco Canyon were abandoned following objections from Indigenous groups, and the Society for American Archaeology had formally written to Netflix about the first season.