During my visit to Peru, the most amazing thing I saw were the ancient Inca stone structures present in areas such as Cusco, the Sacred Valley, and of course at Machu Picchu. In these areas the original structures are still standing today, hundreds of years after their construction. This is a tremendous testament to the skills of the Inca engineers since Peru regularly experiences strong earthquakes that score over 7.0 on the Richter scale. In these earthquakes modern buildings are completely destroyed while the Incan structures remain standing.
To build walls, the Incas used a mortarless construction with irregularly shaped rocks that were placed together much like a jigsaw puzzle. In addition to shaping the rocks to fit together on the wall face, they also carved or grinded the rock surfaces that met to have concave and convex surfaces.
This type of construction is very resistant to earthquakes: The lack of mortar allows rocks to move independently during an earthquake and since the rocks were irregularly shaped they would fall back into their proper place as the earthquake subsided.
In constrast to the Inca stonework, the Spanish used a brick and mortar construction. This had the advantage of being much easier and quicker to build, but would fall apart with any major earthquake. For example, in Cusco the Spanish church built on top of Qoricancha was destroyed by an earthquake in 1950. The Incan foundation remained untouched.
Although we can study the completed Incan structures, the method by which they built them is unknown. The Incans had no written language and any knowledge that would have been passed on to their descendents with an oral tradition was lost after the Spanish conquest. Today, researchers can only guess at the techniques they used and there are no definitive answers to questions such as:
- How did the Incas move stone blocks from the quarry to their construction site? At Sacsayhuaman, many of the blocks are huge and weigh over 100 tons. At Ollantaytambo, the quarry was several kilometers away on the other side of the valley.
- How were the stones cut and shaped so that they would fit together perfectly? In the best stonework, the gap is so small that it would be hard to slide a sheet of paper between the stones.
- How were the blocks lifted and placed into position? The Incan’s did not have access to pulleys and the blocks could weigh many tons.