Physical Security Principles and the Test of Time: A “Forensic Risk Assessment” of Machu Picchu

In the high mists of the Peruvian jungle is an elegant testament to the effectiveness of carefully layered physical security design principles.  It has stood the test of time, the elements, and – most importantly – the Spanish Conquistadores.

It is the Incan citadel known as Machu Picchu (translated “old mountain”), located deep in the Cordillera Vilcabamba, on the eastern slopes of the Andes mountains.  A few weeks ago I visited this remote mountaintop location as a tourist.  Despite my role, I could not help but look at this amazingly beautiful but remote location through the eyes of a potential adversary…imagining “what if” the enemies of the Inca had decided to attack this location.  The exercise was revealing, and prompted different questions to my guide than I suspect he was used to getting from the average tourist.

Most guidebooks emphasize the sacred aspects of Machu Picchu’s location, with respect to Incan religious and cultural traditions.  While these lofty design elements are certainly validated by several features of the site (the Inca combined the political with the religious), I could not shake the feeling that “spiritual inspiration” alone was not the guiding principle behind the tremendous investment of time and effort made by its architects.  So, as I listened with one ear to our well-informed young guide, my inner “security consultant” constantly whispered in the other.   My conclusions are as follows:

First, the context of the time at which Machu Picchu was constructed is important to consider because of the perceived threats of that era.  The Inca Empire was founded on and maintained by brutal force.  It’s existence was relatively brief, from 1433 to 1538.  However, during that time the empire grew to control over 800,000 square miles of territory, with 20 million citizens from half a dozen conquered tribes.  The empire was not popular.  The Inca engaged in forcible resettlement policies with conquered populations, and an aggressive policy of taxation.  At the time that Machu Picchu was conceived and constructed, the empire through its rapid expansion had tangible threats to its power and authority.  The relatively short lifespan of the Incan Empire was marked by constant tribal rebellions, and challenges to authority.

Through the prism of risk assessment, there were three very tangible assets requiring protection.  First, the empire itself.  The lifeblood of the empire was its revenue through taxation.  The gold, silver, goods, and services from tax administration flowed back into the seat of the Inca empire, Cuzco (approximately 50 miles southeast of Machu Picchu) via the well-developed set of roads – now known as the “Inca Trail” – spread out through the vast empire over 15,000 square miles.  The second asset was the Incan king himself.  The king was considered a deity.  A third asset of utmost importance, only two days travel by foot from Machu Picchu, was the Maras salt pans (evaporation ponds).  This particular asset is not mentioned in contemporary accounts of why Machu Picchu was built.  However, to my mind it makes complete sense.  Without Machu Picchu, these incredibly valuable salt pans would be completely exposed to exploitation and capture by adversaries.   Salt was of critical importance to the Inca, as it was used as a preservative for food, to tan hides, and stabilize dyes.  It was so important, that salt and gold was traded pound-for-pound.  These salt pans still exist to this day and are seasonally farmed.


Figure 2 – The Maras Salt Pans, which have been in existence and farmed since pre-Inca and Inca times.  They remain active to this day, and would have represented an incredibly valuable asset to the ancient Incans worth protection.

If we consider vulnerabilities, one very apparent weakness was the approach into what is known as the “Valle Sagrado”, or Sacred Valley.  Without Machu Picchu, a marauding army could use the cover of heavy jungle forest and heavy mist that blankets the steep gorge up the Urubamba River to approach and then raid into the fertile plain of the Sacred Valley, where most of the Inca lived and cultivated crops.  A critical asset would have been the Maras salt ponds, that lie within a small canyon adjacent to the plains and are easily accessed.

Taking the preceding into account, as the burgeoning empire grew in power and influence, it was natural that the Inca rulers of the time realized the need to invest time and treasure into securing their capital and its means for sustenance.   Having visited several Incan sites (including the salt pans at Mara), I was consistently struck at how practical these ancient people were.  The popular explanations about Machu Picchu’s construction for religious or spiritual reasons, or as a “resort” for the Incan kings, did not make sense to me.  What made overriding sense, was the need for a well fortified outpost protecting access routes into and out of the seat of power.  A place that could easily sustain an army, with little or no supply lines required.  Machu Picchu, examined through the prism of five principles of physical security:  detection, delay, deterrence, response (defense) and recovery (resilience), is the perfect location for defense of the realm.

Detection: Machu Picchu was placed on the crest of peak, ensuring a commanding, unobstructed view from three sides of the Urubamba River Valley 1,500 feet below.   This is true both from the city itself, and the heights of the iconic “Huayna Picchu” (Young Mountain) that overlooks the citadel.  Alternatively, the thick jungle forest on the steep slopes below Machu Picchu ensured it was camouflaged from anyone below.   Another interesting feature of Machu Picchu is the Temple of the Sun tower.  This Temple features a window in which the sun’s rays entered at the dawn of the June solstice.   This window is aligned perfectly with the Sun Gate, or “Inti Punku”, the entrance to Machu Picchu from the Inca Trail approximately 1,000 feet above the citadel.   While it is true that at the June solstice the sun’s rays beam directly into this window, it could also have doubled as a location where guards posted at the Sun Gate could easily use reflective signals to the city if someone was approaching along the Inca Trail.  The eastern-facing window in this temple is aligned with Phutuq K’usi, a mountain to the northeast of Machu Picchu across the Urubamba Valley.  An Incan train was recently discovered on this mountain, and as with the Sun Gate, reflective signals could be made to the city from this site by guards if someone was detected approaching.  Of note, the residence of the Incan king and his security entourage are located immediately adjacent to the Temple of the Sun, affording good command and control in the event a signal was received from the remote Sun Gate or Phutuq K’usi guard force.


Figure 3 – Temple of the Sun, with windows aligned to the Sun Gate (guarded) two kilometers to the south and Phutuq K’usi peak to the northeast.

Delay:  A second  element of delay built into the citadel is the Incan system of stone terraces, used to develop steep mountain slopes for agriculture.  These terraces double as significant barriers that would severely hinder a force approaching the city.  Finally, access into the city from the Incan trail is protected by a “trunk bridge” that traverses a 20-foot gap on the trail headed west from Machu Picchu.  When the trunks are removed (like a draw bridge), the route is impassable.

Deterrence:  A force of any size approaching Machu Picchu would, once detected, be easily deterred by the sheer grade of approaches to three sides of the site.  Precipices from Machu Picchu to the valley floor are breathtaking, averaging between 1,500 to 2,000 feet high.  Only an experienced climber could make the ascent, and would easily be detected in the process.

Response (Defense):  A unique feature of the single main approach to Machu Picchu from the Incan trail and the Sun Gate, is a 180-degree bend in the trail that leads up to the gate.  Only one individual at a time can make the turn, and are immediately faced with a steep climb up to the gate.  It is the only way up, and no matter the size of the attacking force, a handful of guards equipped with bows and an adequate supply of arrows could easily hold of the attackers for quite awhile.  Likewise, anyone trying to climb up to the citadel from the Valley below, would be exposed to merciless attack from defenders above.


Figure 4 – A natural spring provides fresh, clean water to this day to the site.

Recovery (Resilience):  This is perhaps one of the best features of Machu Picchu, in terms of its ability to withstand siege or attack.  There is a source of fresh spring water within the citadel that is active to this day.  As mentioned previously, terraces for cultivating and growing staple foods such as potatoes, maize, beets and other vegetables also double as protective barriers to approaches on the crest of the mountain.  There are cleared patches of ground, with soil brought up from below, that serve as grazing pastures for Alpaca, the sturdy Andean animal that can serve as a pack animal, source of wool, and meat.

There is still much debate about why Machu Picchu was really built.  Those who designed and constructed this magnificent wonder of the world are long gone.  Scholars speculate that it could have been a ceremonial center, an administrative city, or just a resort for the Incan king to escape the cold in Cuzco (the ancient Incan capital, located at a much higher elevation than Machu Picchu).  Whatever its purpose, the time-honored principles of security designed and built into this location served to protect its very existence from treasure-seeking Spanish Conquistadors in the 16th Century, and centuries of subsequent invaders. In fact, it remained a hidden treasure until it’s discovery by American Archeologist Hiram Bingham in 1911.   These principles worked to protect the site, and – despite the absence of its long-dead designers – guided my own process of deducing, through use of a disciplined risk review process, what it’s purpose could have been.

Photos courtesy of Charles Goslin