“And I may say, once and for all, carefully weighing my words, that in no part of the world I have seen stones cut with such mathematical precision and admirable skill as in Peru, and in no part of Peru are there any to surpass those which are scattered over the plain of Tiahuanaco.”
[Ephraim George Squier, Incidents of Travel and Exploration in the Land of the Incas, 1877, p. 279]
|Cusco, the famous stone of the twelve angles, masterpiece of megalithic stone masonry. [Photo by Author]|
The megalithic architecture of the Andean altiplano of Peru and Bolivia is indeed remarkable. It has the same clear and neat lines that only ancient Egypt was able to express, and then only briefly over the course of the IV Dynasty of the Old Kingdom. Yet, very often, what is labelled as “Inca architecture” has little if anything to do with the Incas, a people conquered by the Spanish conquistadores in 1533 and whose empire stretching over much of today’s Ecuador, Peru, Bolivia, Chile and parts of Argentina lasted for almost two hundred years since the late XIII Century AD or the beginning of the XIV Century AD. Indeed, most architectural historians and archaeologists have now come to recognize in the megalithic architecture of the Peruvian and Bolivian highlands the legacy of much older civilizations, including the Wari and the Tiwanaku empires, whose history already stretched back several centuries (perhaps even millennia) by the time the Incas became lords of the land.
Over the last couple of decades, architectural historians such as Jean Pierre Protzen and Stella Nair have addressed the mystery of how a civilization with no knowledge of the wheel and which only possessed rudimentary copper tools and chisels could have quarried, transported, dressed and fitted enormous blocks of hard granite, porphyry and andesite stone with the almost supernatural precision that one can see in the ancient sites of Peru and Bolivia. [1,2]
Even though their experiments have been able to shed some light on the techniques that, even with very rudimentary tools, could have been used to craft perfectly planar surfaces, accurate right angles and millimeter wide joints, many aspects of ancient Andean stone cutting and architecture remain unexplained.
One of the most puzzling and debated issues with Andean megalithic architecture is the apparent vitrification of the stone surfaces one notices at several ancient sites. If rocks were indeed vitrified, as some historians claim, their ancient builders ought to have possessed some yet unknown means by which they were able to soften, melt and in some cases vitrify enormous masses of rock, making it extremely easy to carve stone as hard as granite and andesite in any kind of desired shapes and angles.
The most prominent features of these “vitrified” rocks include:
- A shiny, glossy appearance that reflects light like a mirror
- The presence of a “layer” on the surface of the stone, where the apparent vitrification is visible
- Evidence of vitrification in places where it would be illogical or simply impossible to achieve a similar level of polish by any other more conventional technique (such as hammering, chiseling or polishing with an abrasive substance such as sand or quartz powder)
- An evident discoloration or change in color and texture of the stone in areas where the vitrification phenomenon is apparent
- Marks in the stone or other evidence that might suggest that the stone was indeed molten or softened at some point during construction
- The presence of a residual magnetic charge in the stone, detectable by means of a compass (although it is unclear how this might be related to the vitrification observed, if at all)
- The sockets where metal clamps would have been inserted to join together adjacent blocks of stone are often visible in stones that bear traces of vitrification (with the sockets or T-Grooves also showing signs of vitrification)
Below is an overview of some of the anomalies and apparent traces of vitrification we have been able to document at several Peruvian sites.
A set of perfectly aligned windows inside the Qorikancha, the “Golden Enclosure” of ancient Cusco. [Photo by Author]
The Qorikancha, meaning “Enclosure of Gold” was the most important state temple of the Inca Empire, in the heart of their capital city of Cusco. The ruins of the Qorikancha survive underneath the modern day church and convent of Santo Domingo, and are universally recognized as one of the finest examples of Inca stonework in the so-called “Imperial style” using large, squared blocks of granite or andesite. Indeed, a number of elements may suggest an even older origin for the temple, perhaps dating back to the time of the Wari and Tiahuanaco empires (these include the presence of T-Grooves designed to host metal clamps, typical of Tiahuanaco architecture but absent from Inca construction techniques, as well as some controversial astronomical alignments that might point to an even earlier construction date. )
The architecture of the Qorikancha is both imposing and austere. The interior is divided in a number of rooms facing a central courtyard, while the outer walls rest on an imposing series of terraces towards the river Huatanay (now little more than a streamlet), that culminate in an impressive curved wall likely built for some astronomical purposes. The stones that compose this outer wall show a remarkable degree of polish. Although these stones do not bear any clear signs of vitrification, their almost metallic finish and mirror-like polish is indeed remarkable.
The beautiful curved wall outside the Qorikancha, overlooking the valley of the river Huatanay. It was likely used for astronomical observations and also hosted a solar gnomon called a Intihuatana. [Photo by Author]
The wonderful outer wall of the Qorikancha facing Calle Ahuacpinta. It is possible to appreciate the very tight joints and the indenting between the stones.
|Another view of the outer wall of the Qorikancha facing Calle Ahuacpinta. The horizonal joints are also vitrified. [Photo by Author]|
The outer wall facing Calle Ahuacpinta is perhaps the most remarkable as it shows a number of features that testify to the extreme skill of the ancient stonemasons. The wall is entirely built of pinkish-gray granite, using neatly fitted and joined rectangular blocks. Even though the vertical joints are rarely perpendicular, the horizontal joints run almost perfectly straight.
If observed from close enough, however, the joints reveal something truly remarkable. First of all, each stone possesses a slight, almost imperceptible indentation, so that even the horizontal joints are never truly horizontal, but designed in such a way that each stone would be “locked” in place by means of tiny indentations in each of the adjoining stones. Nevertheless, the joints are so tight as to be barely visible and not even the proverbial sheet of paper could be fitted in between two stones.
The amount of work required to achieve such a perfect fit while keeping tiny indentations between the blocks would be unconceivable by any modern standard, and can only find justification in the high seismicity of the region (perfectly horizontal and perpendicular joints would have caused the stones to slide during an earthquake, while the tiny indentations would have kept them tightly into place). In addition to this very peculiar fit between the blocks, the joints (especially the horizontal joints) appear to be vitrified. A shiny, vitrified layer can be seen at night between the joints or by pointing a flashlight parallel to the wall. There is no explanation as to how this level of vitrification was achieved or why. From a structural point of view, however, the vitrification of the joints would have conferred the wall an almost indestructible strength making it extremely resistant even to the most violent earthquakes.
Vitrification, however, is not limited to the joints. A few stones in the interior of the Qorikancha also show evidence of glazing as if covered by a vitrified film or layer that reflects light. Oddly enough, this coating seems to have been hammered or chiseled away at some point, leaving the stone with a much rougher appearance (why or when this was done remains the subject of speculation, although this might be a consequence of the walls being stuccoed and painted during colonial times).
A dark corridor inside the Qorikancha well expresses the severe and monumental character of this structure. [Photo by Author]
A partially vitrified stone block inside the Qorikancha. Interestingly, the vitrified layer seems to have been deliberately hammered and chiseled away at a later date, possibly during colonial times. [Photo by Author]
A remarkable niche inside the Qorikancha, with drilled holes and mysterious grooves. [Photo by Author]
The gigantic fortress of Sachsaywaman dominates the city of Cusco from a hill. Some of the stones used for its construction weigh in excess of 250 to 300 tons, and are fitted together with remarkable accuracy. Many of the stones employed in the construction of the fortress appear molten, as if they had been artificially softened and fitted into place, some of them even bearing partially vitrified “scars” suggestive of the application of very intense, concentrated heat.
One of the megalithic gateways leading into the great fortress of Sachsaywaman, above the city of Cusco [Photo by Author]
Some of the strange marks or scars visible on certain stones at Sachsaywaman appear to be the product of intense heat applied to the stone and are also partially vitrified. [Photo by Author]
The most remarkable signs of vitrification are however found on rocks on the hill facing Sachsaywaman (called Rodadero because of the round shape of the vast stone amphitheater that was carved into its summit). A particular rock platform called the “Throne of the Inca” has perfectly planar, partially vitrified surfaces cut in steps, which also appear to be heavily magnetic. Many of the nearby stones are also carved into steps, often forming long stairways, niches and altars.
The “Throne of the Inca” facing the fortress of Sachsaywaman, on the hill of Rodadero. The steps show signs of at least partial vitrification and bear significant magnetic anomalies. [Photo by Author]
A vitrified tunnel near the Chincana Chica on the hill of Rodadero. Not the mirror polish on the walls and on the ceiling. [Photo by Author]
Cusco – Q’Enko
The great cave of Q’Enko. The surfaces of the altars and tables show clear signs of having been vitrified. [Photo by Author]
|A detail of a vitrified stone surface on the side of one of the altars in the cave of Q'Enko. Vitrification appears as a thin layer on the surface of the stone. [Photo by Author]|
Q’Enko is located on a rocky outcrop a short distance from Sachsaywaman and is divided in two areas called Uchuy Q’Enko (meaning “Little Q’Enko) and Q’Enko proper. Uchuy Q’Enko has more of the strangely carved rocks and cyclopean walls reminiscent in style of the constructions of Sachsaywaman. The rock surface contains many carvings that might have once been chambers and corridors that are now open to the air and badly weathered. The extreme weathering of the stone is even more puzzling if one considers that it is entirely composed of very hard andesite stone, a rock very similar to basalt. One particular trench cut into the rock is very much suggestive of a portcullis system connected to a small canal, with parallel grooves clearly visible on both sides of the trench.
The main cave of Q’Enko, believed to be used in funerary rituals, contains several tables and altars (for lack of any other suitable functional explanation) whose surface is entirely vitrified.
Cusco – Temple of the Moon (and Temple of the Monkeys)
The little know Temple of the Moon (and the nearby Temple of the Monkeys) are two rarely visited sites located in the vicinity of Q’Enko. The so-called Temple of the Moon is in fact a large rocky outcrop containing many caves where altars and other structures have been carved into the living rock. The most remarkable of these caves, containing a large ceremonial platform or altar and accessed through a short descending stairway, is entirely vitrified both on the walls and the ceilings. Vitrification of the rock surface is so extensive that the stone shines and reflects the light like a mirror. One can see his own image reflected on the walls and the ceiling as if they were entirely made of polished glass. Similar traces of vitrification are also found on a large altar inside the Temple of the Monkeys, where erosion has left exposed a system of underground chambers and passageways.
The steps leading into the cave of the Temple of the Moon. Note the mirror-like reflection of the stairway on the left wall. [Photo by Author]
Another view of the cave of the Moon, from inside. All the walls and ceilings are entirely vitrified. [Photo by Author]
A view of the Temple of the Moon, from the outside, carved into a rocky outcrop a short distance from Q’Enko. It is possible to see what were clearly the walls and ceilings of chambers that are now entirely exposed to the elements. [Photo by Author]
The great fortress of Ollantaytambo rests on a steep terraced hill dominated by the gigantic megalithic walls of the temple of the Sun, guarding one of the accesses to the Sacred Valley near Cusco.
Ollantaytambo is most famous for the six giant porphyry megaliths, each weighing in excess of 70 tons, which form the façade of the Temple of the Sun (the original appearance of this massive megalithic structure is still the subject of speculation). Similar to the Qorikancha, Ollantaytambo shows signs of different epochs of construction, with the megalithic phase being the earliest and the most refined. Enormous blocks of stone lie scattered around the summit and at the base of the hill, many of which were later reemployed in the much cruder construction of the late Inca period. Interestingly, some of the stones must have been already badly weathered and damaged when they were reused. Several stones also possess T-grooves for holding metal clamps, which are strongly reminiscent of Tiahuanaco architecture.
Smaller stones were inserted between the larger megaliths, possibly for aesthetic or symbolic reasons. The joints between the smaller stones and the larger monoliths are also vitrified. [Photo by Author]
A T-Groove can be seen on a large porphyry stone lying in front of the megalithic wall of the Temple of the Sun. Also note the thin vitrified layer covering the left side of the stone. [Photo by Author]
A perfectly drilled hole in a fallen block of porphyry at Ollantaytambo. Notice the thin grooves and tool marks left inside the hole. [Photo by Author]
The cyclopean masonry leading up to the top of the hill is the finest in Peru, showing a level of polish and accuracy which is almost unparalleled in the ancient world and gives it the appearance of polished metal rather than stone. The protruding bosses that one can see on the surface of many of the stones (and which are also a prominent feature in megalithic buildings in Cusco and elsewhere) were certainly used for the lifting and transportation of the colossal blocks of stone, even though one wonders at the reason why they were left to protrude out of the stone even after the stones had been dressed and fitted into place. Perhaps construction was abandoned and the building was left unfinished at some early stage of completion, but this is hard to reconcile with the degree of polish and the perfect finish of other parts of the wall.
Among the stones found at Ollantaytambo are pink-red porphyry, gray andesite, black basalt and diorite. No doubt, the chromatic effect of so many different colored stones would have been beautiful. The joints between the stones, including the largest monoliths, appear to have been vitrified as they are coated in a thin reflective layer. This can clearly be observed where certain stones have been removed from the construction. Not only was the edge of the joints vitrified, but the whole stone surface experienced a similar process. What is interesting is that vitrification was apparently limited to the joints or the contact surface with the adjoining stones, but is not usually present on the outer face of the stone (which is polished, but not vitrified). This would suggest two rather obvious conclusions at this point:
- Vitrification served some functional or structural purpose, and was not done for aesthetic reasons (otherwise the outer face of the stone, the only one that would have remained visible, would have been subject to vitrification too)
- Vitrification, being only superficial and only in portions of the stone that would have been hidden from sight and therefore not exposed, must be intentional and not the consequence of fire or another catastrophic event
One last point of contention is whether the vitrified layer is indeed part of the stone or rather constitutes a separate vitreous substance applied to the stone (perhaps as a sort of cement or concrete).
This last question is not easily answered. Even though the vitrified surface appears almost as a layer on the stone, it nevertheless appears to be the result of some physical or chemical transformation of the stone itself rather than being just attached to it. Also, vitrification is not only found in masonry, but also in the natural bedrock, in caves and tunnels.
Sadly, very little analysis has been done to determine the composition of the vitrified layer and whether it is chemically or physically different from the stone itself. Some samples collected from a set of vitrified caves and tunnels at a site called Tetecaca, above the city of Cusco were purportedly analyzed by the University of Utrecht, Holland. Microscope photographs have revealed two clearly distinct regions, the vitrified layer and the stone underneath. The presence of a transition layer, which is also clearly visible in photographs, suggests however that the vitrified surface and the stone body are not separate but are indeed one and the same, although the surface of the stone has certainly undergone a physical transformation.
Interestingly, however, the chemical composition of the surface layer appears to be at least partially different from that of the body stone, as it contains elements not present in the natural rock samples. This suggests that a kind of glaze composed of mostly silica was applied to the stone under conditions of extreme heat and pressure. 
Even if these results were confirmed with more evidence from other sites, it remains to be explained how a similar glaze could be applied to the stone and how the required temperatures (well above 1,000 degrees Celsius) and pressures could be reached and maintained in the open air outside of a large furnace.
Note: Other vitrified stones are found in the city of Cusco itself and in the nearby sites of Tambomachay, Chincheros and the “Zona X” (which will be the subject of a future article). Vitrified stonework is also found at Machu Picchu, although limited to the joints between the stones of the Temple of the Three Windows and the Main Temple plaza.
 Jean Pierre Protzen, Inca Architecture and Construction at Ollantaytambo, Oxford University Press, 1993
 Jean Pierre Protzen and Stella Nair, The Stones of Tiahuanaco: A Study of Architecture and Construction, The Cotsen Institute of Archaeology Press, 2013
 Rolf Muller, Die Intiwatana (Sonnenwarten) im alten Peru, Berlin, Verlag von D. Reimer, 1929
 Jan Peter de Jong, Evidence of Vitrified Stonework in the Inca Vestiges of Peru, http://janpeterdejong.weebly.com/vitrified-stones.html