Sacsayhuaman is an Inca walled complex near the old city of Cusco. The site is part of the City of Cuzco, which was added to the UNESCO World Heritage List in 1983.

Some believe the walls were a form of fortification, while others believe it was only used to form the head of the Puma that Sacsayhuamán along with Cuzco form when seen from above. Like much Inca stonework, there is still mystery surrounding how they were constructed. The structure is built in such a way that a single piece of paper will not fit between many of the stones. This precision, combined with the rounded corners of the limestone blocks, the variety of their interlocking shapes, and the way the walls lean inward, is thought to have helped the ruins survive devastating earthquakes in Cuzco. The longest of three walls is about 400 meters. They are about 6 meters tall. Estimated volume of stone is over 6,000 cubic meters. Estimates for the largest limestone block vary from 128 tonnes to almost 200 tonnes.

The Spanish harvested a large quantity of rock from the walls of the structure to build churches in Cuzco, which is why the walls are in perfect condition up to a certain height, and missing above that point. Sacsayhuamán is also noted for an extensive system of underground passages known as chincanas which connect the fortress to other Inca ruins within Cuzco.

On March 13, 2008, archaeologists discovered the ruins of an ancient temple in the periphery of Sacsayhuaman; it is believed to have been built by the Killke culture which occupied the site between 900 and 1200 AD.

Vince Lee is an Author Architech and explorer who has been consulted on various ancient sites that moved large megaliths. He theorized that the blocks were put into place by carving them first and then lowering them into place. This would have involved doing precise carving ahead of time to create the tight joints that are made to fit into prepared pockets existing in the wall. Then they would be towed up a ramp and above the wall where they would be placed on top of a stack of logs. Then the logs would be removed 1 at a time to lower the stones into place carefully. An experiment was done to see if this would work on a small scale; this accomplished limited success. In the event that they were unable to obtain the tight joints the first time the Incas would also have been able to lift the stones back up to correct their mistakes. They were not able to obtain as much precision as the Incas but they theorized that with more practice they could have accomplished more precise joints and done it with larger stones.

They also did several experiments in nearby Ollantaytambo to tow megalithic stones. This also led to limited success. They conducted one experiment where they tried to lower a 1 ton stone down a mountain. They lost control of this stone and it rolled down on its own. This is probably not the way the Incas did it since they would have wanted to control the transportation and this could have led to a lot of accidents. They concluded that although they had gravity on their side they had to practice to maintain control of the decent. They also did an experiment towing a megalith that may have been close to 10 tons on cobblestones. They had about 12 people behind the megalith pushing it while well over 100 people were pulling on several ropes to tow it. They succeeded in towing it at a fairly quick pace. The ancient Incas built a large road system that included 25,000 km of roads. Some of these roads were embellished with stone pavings.