The architectural mastery of the great Inca civilization mystifies archaeologists around the world. To illustrate, the Twelve Angle Stone of Hatunrumiyoc in Cusco is one of the most sophisticated examples of their ingenuity, with its 12 angles fitting seamlessly into the surrounding wall. It was laid by Inca masons over 700 years ago, and today is considered a National Heritage Object. The material is a green diorite igneous rock and it is about six feet deep and weighs six tons.

The significance of the 12 angles is not widely known, but it is believed to represent the division of 24 families of Cusco: 12 during the Hurin dynasty and 12 during the Hanan dynasty. The stone was originally part of the Inca palace called Palacio Inca Roca. In the early 20th century, it became the Archbishop’s palace.

The perfectionist Inca stonework is remarkable. This is because they laid the stones so precisely that the use of mortar to hold them together was not necessary. In fact, so perfectly the stones fit, that a piece of paper would not fit between them. As a result, their constructions were also so stable, that they would simply “dance” and then resettle in the event of an earthquake. The 12-angle stone is the most complex example of this puzzling precision.

Twelve Angle Stone of Cusco numerated. Image by Ian Burke.