At an elevation of more than 12,000 feet in the northern outskirts of the city of Cuzco, Peru, we find the ancient fortress of Sacsayhuaman whose immense stone walls are believed to hold secrets which predate the Inca themselves.

Surface collections and analysis of pottery at Sacsayhuaman indicate that the earliest occupation of the hill top dates back at least a millennium, making it one of the oldest ancient establishments on the planet.

The fortress was the largest structure built by the Incas. It was constructed on an elevated rocky promontory facing the northern marshy ground outside the Inca capital of Cuzco. Pottery finds indicate that the site had previously been occupied by Inca residents.

Begun in the reign of the great Inca empire builder Pachacuti Inca Yupanqui, or perhaps his son Thupa Inca Yupanqui in the mid-15th century CE, the design was credited to four architects: Huallpa Rimachi, Maricanchi, Acahuana, and Calla Cunchui.

The first structures were made using only mud and clay. Subsequent rulers then replaced these with magnificent stonework which employed huge finely-cut polygonal blocks, many over 4 metres in height and weighing over 100 tons.

To complete such a massive project 20,000 labourers were drafted in under the well-established Inca system of extracting both goods and labour from peoples they conquered. Working in a system of rotation 6,000 were given quarrying duties while the other 4,000 dug trenches and laid the foundations.

The walls of the fortress were built in vertical sections, probably, each section being the responsibility of one ethnic labour group. According to legend, some 3000 lives were lost when one huge stone that was being dragged uphill broke free.

The Incas were master stonemasons. Huge blocks were quarried and shaped using nothing more than harder stones and bronze tools. Marks on the stone blocks indicate that they were mostly pounded into shape rather than cut.

Blocks were moved using ropes, logs, poles, levers, and earthen ramps ( marks can still be seen on some blocks), and some stones still have nodes protruding from them or indentations which were used to help workers grip the stone.

Sacsayhuaman played an important part in the final defeat of the Inca Empire by the Spanish. Pizarro’s party entered Cusco unopposed in 1533 and lived there securely for more than two years before finally being caught unprepared by the rebellion of Manco Inca in 1536.

Manco’s troops took the fortress of Sacsayhuaman, overlooking the city, and used it as his base to attack the Spanish. After weeks under siege in the city the Spanish broke out and charged into the surrounding hills to the northwest above the city. They then doubled back to capture the rocky outcrop opposite the fortress.

From this outcrop they made repeated attacks across the flat plaza against the walls of the fortress. All the Spanish reinforcements on their way from Lima to Cusco had been massacred, so if the Spanish failed to take the fort they were doomed. In the evening, against all odds, the Spanish eventually broke through the Inca defenses and scaled the walls of the fort driving the defenders into the fortified complex dominated by 3 towers (foundations only remain today).

After two more days of fighting the Conquistadors finally overwhelmed the natives, putting them all to the sword. It was said that during the battle a leading Inca nobleman, armed with a Spanish sword and shield, caused havoc by repulsing every enemy who tried to scale the last tower left in Inca hands. Having sworn to fight to the death, he leapt from the top of the tower when defeat was inevitable, rather than accept humiliation and dishonour