The Inca capital and the Spanish city built on top of it: the Temple of the Sun under a monastery, what earthquakes left in its walls, how the twelve-sided stone was fitted without iron, and who really laid out the straight streets.
In one street of the Peruvian city of Cuzco, a single block in an Inca wall has twelve cut sides, each fitted tight to a neighbouring stone with no mortar between them. The masons who shaped it had no iron tools. Cuzco lies in a valley in the Andes of southern Peru, about 3,400 metres above sea level, and in its old centre straight streets still run between walls of fitted stone, many of them carrying Spanish colonial buildings on top. The stone and the street plan are older than the buildings above.
The Inca capital
The Inca city took its shape in the fifteenth century, when the ruler Pachacuteq redesigned Cuzco as the capital of Tawantinsuyu, the Inca empire, which came to cover much of the Andes. At its heart lay the main square, Hawkaypata, and from it four main roads set out, each into one of the four regions of the empire.
The centre held temples and the walled residences of the royal families; most other people lived outside it. The religious heart was the Qoricancha, the Temple of the Sun, dating from the fifteenth century. Its walls were covered with gold, and inside was a garden made of gold. Sacred lines called ceques ran from it to shrines across the Cusco valley. Unlike ordinary Inca walls, its walls were laid in even rows of rectangular blocks with smooth faces. The wall with the twelve-sided stone belonged to a different building: the palace of Inca Roca, an earlier ruler.
A city on top of a city
Spanish forces under Francisco Pizarro took Cuzco in 1533 and stripped the Qoricancha of its gold. Dominican friars took over the site and built the church and monastery of Santo Domingo on top of the temple, reusing its foundations and some of its walls. Inca Roca's palace went the same way: the Spanish built the archbishop's residence over what was left of it, and the Inca wall became its foundation. Across the city the newcomers kept the Inca street plan and raised their own buildings on Inca foundations. At Santo Domingo the two still stand together, and parts of the Inca temple can be seen within the monastery.
Two great earthquakes stand out in Cuzco's written history, in 1650 and 1950, and both did heavy damage. The 1950 earthquake damaged the church at Santo Domingo and exposed Qoricancha walls it had hidden for about four centuries. Inca stonework came through 1950 with little damage: the mortarless stones held, while mortared colonial walls were damaged. A team led by Andy Combey of the University of Grenoble Alpes, working with Peru's national geological institute, surveyed Inca stonework at sites around Cuzco and logged thousands of earthquake marks. Some blocks are fractured; others have broken corners or have been knocked out of line. The damage runs in a consistent direction across the region, pointing back to the direction of the shaking. In it the researchers read two strong earthquakes, one of which seems to have struck in Inca times and appears in no written record.
How the twelve sides happened
Hatunrumiyoc is a street in the old centre. Along it runs a wall of many-sided stones, each shaped to fit those around it: a retaining wall of Inca Roca's palace, with the archbishop's residence on top. The architecture professor Jean-Pierre Protzen studied Inca walls around Cuzco and tested the methods himself. In an old Inca quarry he found rounded river stones that the masons had used as hammers.
The biggest hammerstones break the block out of the rock, smaller ones shape the faces, and the smallest work the edges so they don't chip. Surfaces are worked by pecking, and Inca stones still carry the marks. For the fitting, the seat for each new block is cut into the stone already laid below it. The outline of the new block is marked on the lower stone, the seat is pounded out, and the block is lowered on. Where the stones touch, the dust of the pounding is pressed flat; elsewhere it stays loose. The pressed spots are the high points, so the block comes off, those spots are pounded down, and it goes back on, again and again until the joint closes. It is trial and error. Protzen finished his own test joint in a matter of hours. Because each block was fitted to whichever stones were already beside it, blocks end up with varied numbers of sides. Protzen called the twelve angles "the simple result of the fitting technique".
Why it's on the list
UNESCO inscribed the City of Cuzco in 1983 on two grounds. It is a unique testimony to Inca civilisation and its imperial government, and the sum of some 3,000 years of indigenous cultural development in the southern Andes, with walls of carefully cut granite or andesite and straight streets between them. It also shows the meeting of Inca and Hispanic cultures: the Inca structure was kept and the Spanish built their religious houses and mansions over it, producing a city plan and architecture found nowhere else.
That record also answers a common assumption, that Cuzco's straight streets were a Spanish layout. UNESCO describes the Inca city itself as one of straight streets within stone walls, and the grid of the colonial and modern town still follows the Inca plan.
In one street of the Peruvian city of Cuzco, a single block in an Inca wall has twelve cut sides. Each side is fitted tight to a neighbouring stone, with no mortar between them. The masons who shaped it had no iron tools.
This is Ours to Keep. I'm Mira, and today: the City of Cuzco. I'm an AI voice; the facts come from official records and checked sources.
The Inca capital
Cuzco lies in a high valley in the Andes of southern Peru, about three thousand four hundred metres above the sea. In its old centre, straight streets run between walls of fitted stone. Many of those walls carry Spanish colonial buildings on top. The stone at the bottom is older than the buildings above it, and the street plan is older too.
The Inca city took its shape in the fifteenth century. The ruler Pachacuteq redesigned Cuzco as the capital of an empire the Incas called Tawantinsuyu. It came to cover much of the Andes. Machu Picchu, where this week began, is thought to have been one of his royal estates.
Inca Cuzco was split in two, into an upper half and a lower half. At its heart lay a great main square. Four main roads set out from that square, and each one ran into one of the four regions of the empire. Those four roads were the trunk of a great Inca road network, and Cuzco sat at its centre. The centre was not where most people lived. It held temples and the walled homes of the royal families, and most other people lived outside it.
The city's religious heart was the Qoricancha, the Temple of the Sun. The temple dates from the same century as Pachacuteq's new capital. Its walls were covered with gold. Inside, there was a garden made of gold. Sacred lines ran out from the temple to shrines all across the valley around the city.
The temple was built differently from most of the city. Ordinary Inca walls were fitted stone by stone, so their blocks came out in all sorts of shapes. The Qoricancha's walls were laid in even rows of rectangular blocks, with smooth faces.
Not every great wall in the centre was a temple wall. One of them was part of the palace of an earlier ruler, Inca Roca. That is the wall with the twelve-sided stone, and we'll come back to it.
A city on top of a city
The Inca capital did not stay in Inca hands for long. In 1533, Spanish forces under Francisco Pizarro took Cuzco. Soon afterwards, Pizarro made Manco, a son of an earlier Inca ruler, lord, and ordered the local chiefs to obey him. The next year, one of the Spaniards, Pedro Sancho, wrote about what he had seen. He called the city so great and so beautiful that it would be worth seeing in Spain.
The conquerors stripped the Qoricancha of its gold. Dominican friars took over the site, and they built the church and monastery of Santo Domingo on top of the temple. They reused its foundations and some of its walls. Inca Roca's palace went the same way. The Spanish built the archbishop's residence over what was left of it, and the old Inca wall became its foundation.
This happened across the city. The newcomers kept the Inca street plan. They raised their own churches and grand houses over the Inca city, and they set them on Inca foundations. At Santo Domingo, the two still stand together. Parts of the Inca temple can be seen inside the Dominican monastery.
What the walls remember
Cuzco sits in earthquake country, and two great earthquakes stand out in its written history. The first struck in 1650 and did heavy damage to the city. The second came in 1950, and again the damage was heavy.
The 1950 earthquake did something else as well. At Santo Domingo, it damaged the colonial church and exposed walls of the Qoricancha that the church had hidden for about four centuries. Across the city, the Inca stonework came through with little damage. The fitted stones held together, while the mortared colonial walls above them were damaged.
Little damage is not the same as none. A team led by Andy Combey of the University of Grenoble Alpes in France, working with Peru's national geological institute, has surveyed Inca stonework at sites around Cuzco, and they logged thousands of marks left by earthquakes. Some blocks are fractured. Others have broken corners, or have been knocked out of line. The damage runs in a consistent direction across the region, like an arrow pointing back to the shaking. The researchers read in it the marks of two strong earthquakes. One of them seems to have struck in Inca times, and no written record mentions it.
Up close
So let's stand in one street in the old centre, Hatunrumiyoc. Along one side runs a wall of many-sided stones, each one shaped to fit the stones around it. This was a retaining wall of Inca Roca's palace, and the archbishop's residence now stands on top of it. Partway along is the stone with twelve sides, fitted tight against its neighbours. The wall holds together with no mortar at all.
How do you make a joint like that without iron? An architecture professor, Jean-Pierre Protzen, set out to find out. He studied Inca walls in and around Cuzco, and he tested the methods with his own hands. In an old Inca quarry, he found rounded stones from a river. The masons had used them as hammers.
The work is pounding, not carving. The biggest hammerstones break the rough block out of the rock. Smaller ones shape the faces. The smallest are used on the edges, so the edges don't chip. Every surface is worked by pecking, blow after blow, and Inca stones still carry the small marks of it. No metal chisel is needed for any of this.
Then comes the fitting. The stone below is already in place, and the seat for each new block is cut into the stone beneath it, not into the block itself. The outline of the new block is marked on it, and the mason pounds out that seat. The new block is lowered onto that seat. Where the two stones touch, the dust of the pounding is pressed flat. Where they don't touch, the dust stays loose. The pressed spots show the high points. The block comes up again, and the mason pounds those spots down. Then it goes back on, and back off, and back on, until the joint closes. It is trial and error. Protzen finished his own test joint in a matter of hours. Then the next block goes on, and the same work begins again.
Seen this way, the twelve sides are not a puzzle someone worked out in advance. Each block was fitted, one by one, to whichever stones were already beside it. So blocks in walls like this one end up with all sorts of numbers of sides. The famous stone simply met more neighbours than most. Protzen put it plainly. He called the twelve angles the simple result of the fitting technique.
Why it's on the list
So why is it on the list? UNESCO gives two reasons. The first is that Cuzco is a unique witness to Inca civilisation and to the government of its empire. UNESCO sees in the city the sum of some three thousand years of indigenous cultural development in the southern Andes. The record describes an Inca city with clearly defined religious and government areas, and exclusive homes for the royal families. It sets farming and craft production apart, in their own clearly marked areas. It points to walls of carefully cut granite or andesite, with straight streets running between them. And it notes that the city still keeps the layout of its Inca years.
The second reason is the meeting of two cultures. After the conquest, the Inca plan was kept, and the Spanish raised their religious houses and mansions over the Inca city. In UNESCO's view, that meeting produced a blend of cultures, and a city plan and architecture found nowhere else. The City of Cuzco was inscribed on the World Heritage List in 1983.
The surprise
It's easy to assume that Cuzco's straight streets were laid out by the Spanish after the conquest. The UNESCO record says otherwise. UNESCO describes the Inca city itself as a place of straight streets running between stone walls, and the Spanish kept that plan when they built. The grid of the colonial town, and of the modern one, still follows the layout of the Inca capital. So the churches came with the Spanish, but the straight streets between them were already there when they arrived.
Next week, we cross the ocean to Italy, for five more places and traditions that the world has agreed are worth keeping.
