High in the Andes Mountains of Peru is the ancient city of Machu Picchu, straddled between granite peaks and surrounded by tropical forest. It is 8,000 feet above sea level and its two hundred (+-) stone structures are built over two earthquake faults. Not exactly the kind of place you would expect to find one of mankind’s most impressive engineering feats.
Built by the Inca Empire between 1450 and 1540 AD, Machu Picchu continues to inspire awe in all who sees it, just as it did when it was first established. Most historians believe it was used as a retreat for royalty, perhaps to escape the summer heat of the capital city, then Cusco.
The Inca were master engineers and road builders. An elaborate water-carriage system was installed throughout the city to deliver fresh spring water to inhabitants. It was just as important to properly manage water drain-off caused by heavy rainfall since the Inca understood that water could otherwise severely undermine the city. They accomplished this by excavating deep under the main plaza and depositing a layer of rock in the very bottom before adding a layer of sand and gravel and then the topsoil that would ultimately carpet the plaza surface. The rock the Inca employed in this ingenious drainage system was stone waste created by carving blocks in the quarry (early recycling at its best!).
Another great invention on the part of Inca engineers was the terraced garden. In order to feed local residents crops were grown in plots carved right into the mountainsides. These gardens were designed in the same manner as the central plaza, with layers of soil, sand, gravel and rock waste that would maximize drain-off. But the terraces did more than provide farmland at a high altitude – they stabilized the entire foundation of the ancient city by minimizing erosion. Amazing!
Machu Picchu’s granite quarry from which stone was cut to construct temples, palaces, homes, fountains and walls was located right on the site. Close examination of its structures reveals that the Inca used a stone construction method known today as dry stack. Stone blocks were first carved in the quarry so that they would be matching, like pieces of a puzzle. When the stones were moved to the building site they interlocked seamlessly when stacked – not even a knife blade could be inserted between them! No mortar was needed, thus the name dry stack.
The fact that no mortar was used was an advantage since Machu Picchu is situated on active earthquake faults. When tremblers struck, the dry stack construction was flexible and allowed the stones to move without tension. The effectiveness of this method is a testament to the advanced understanding of the Inca engineers. It is part of the reason why Machu Picchu remains standing today, more than five hundred years later.
For more information and history about Machu Picchu visit: http://www.pbs.org/wgbh/nova/ancient/ghosts-machu-picchu.html