A visit to the former Inca Empire reveals epic feats of construction and engineering that have withstood the test of time, all made without iron tools or draft animals. Over the course of several hundred years, building on practices inherited from previous cultures, the Inca mastered numerous building techniques, particularly stone masonry, to construct and manage a thriving empire that covered some of the most varied landscapes in the world.
Building Blocks
Over a period of several hundred years, the Inca expanded beyond Cusco, gradually taking over neighboring territory and conquering or integrating other cultures in the region. Most scholars agree that what is today considered “Inca architecture” was actually developed over centuries by incorporating, adapting, and refining techniques and styles from groups like the Chavín and Moche.
For many years, similarities between Inca architecture and the remnants of the buildings of the Tiwanaku culture led scholars to believe this group was the primary influence on Inca construction. However, a period of several hundred years between the collapse of Tiwanaku and the rise of the Inca, as well as distinct differences in stone masonry methods revealed by deeper study, have led some scholars to suggest any direct connection is unlikely, though the site may have inspired the Inca to refine their own masonry techniques.
What Makes It “Inca Architecture?”
German explorer and naturalist Alexander von Humboldt, who traveled through the Andes in 1802, wrote that Inca architecture could be described in three words: solid, simple, and symmetrical. Centuries of research since then have revealed far more details about Inca architecture and engineering, but his original assessment still holds true—the Inca constructed solid, sturdy buildings, with little ornamentation and symmetrical configurations.
Today, however, other distinctive features have been identified that differentiate the architectural engineering and style of the Inca from both earlier cultures and other pre-conquest civilizations. One notable difference is that, while pyramidal shapes were used in some structures, the Inca did not build “great” step pyramid temples like their neighbors to the north or earlier cultures in the same region—the Lima culture’s Huaca Pucllana for example.
The common layout for sites throughout the empire was the kancha, a rectangular enclosure with multiple one-story buildings inside that opened onto a central courtyard. Though legend has it that Qorikancha, the Inca Temple of the Sun in Cusco, was once covered in sheets of gold, buildings themselves, from palaces to temples, were constructed with little ornamentation, save double or triple jambs around doorways of particularly important structures.
A subtle element of Inca architecture that sometimes goes unnoticed is the use of trapezoidal shapes. Doorways, niches, and windows (though these were a less common feature of Inca structures) were not rectangular but had narrower tops and wider bases. Walls were often wider at the base than the top as well. Scholars suggest this was a feature that helped buildings not only withstand earthquakes but also improve their structural integrity when built on steep slopes.
The most distinctive feature by far, though, was the precision stone masonry the Inca mastered.
Masters of Stone Masonry
While everyday homes and ordinary buildings were often constructed of field stones or adobe, depending on what was available in a particular region, what stands out most from Inca architecture are the massive constructions using large stone blocks. Without iron, draft animals, or slave labor, the Inca managed to quarry, transport, shape, and assemble enormous stone blocks into impressive structures, many of which are still standing today, the most famous, of course, being Machu Picchu.
One known Inca method for cutting through rock without iron was rather ingenious, in that it required comparatively limited physical exertion. Rather than hacking at the stone with large tools, the Inca would identify natural fissure lines and make small cracks along them. A piece of wood was then inserted into the crack and soaked with water. The water would expand the wood, and this pressure would further crack the stone. The process was repeated with progressively larger pieces of wood until the stone was cracked open completely. Stone blocks were then precisely shaped with copper or stone tools and polished, possibly with sand.
Perhaps the most notable thing about the Inca style of masonry is that it used no mortar, dry masonry called caninacukpirca. Large blocks were shaped to fit together seamlessly, so tightly that a piece of paper cannot be slipped between them, even today. That is not to say that the blocks themselves were perfect cubes or prisms; on the contrary, a visit to any of the Inca’s most spectacular constructions reveals stone blocks of varied shapes, including the famous twelve-angled stone in Cusco. Their method of working with the natural shape of the quarried stone created these unusual shapes and may have added to the sturdiness of their constructions, better distributing pressure or energy from earthquakes.
Without mortar, stones had to be carefully honed to fit together precisely, which suggests that Inca construction relied on detailed measurements and strict planning. Archeologists have noted that some structures, like the qullqa storehouses spread throughout the empire, had a standardized design. This would have required the creation of some kind of “blueprint” that could be shared with various sites, likely recorded on quipus.
Division of Labor
Some of the greatest construction projects of the ancient world relied heavily on slave labor, but despite the challenges the Inca faced, with no horses for lugging stones or iron tools to speed masonry work, slavery was not practiced in their empire. Instead, the Inca relied on a system called mit’a, in which its citizens were required to provide some form of labor to the government each year, in exchange for the government’s care and protection—a kind of tax in the absence of currency.
Men aged 15 to 50 were required to donate a portion of their time to the empire’s various construction projects, everything from the Sapa Inca’s palace to roads, bridges, and storehouses. Mitayos rotated regularly so the work was evenly distributed among the empire’s citizens, and administrators were charged with ensuring laborers still had sufficient time to handle their personal and home life responsibilities—though some scholars argue that the nobility exploited the system.
Chief among their tasks would have been moving the colossal stones used to build magnificent temples, palaces, and fortresses—without horsepower. With stones possibly weighing more than 150 tons, this was no easy task. Researchers suggest a combination of manpower, heavy-duty ropes, and inclined planes was used to move the stones around, as well as employing materials like gravel to reduce friction.
Working With Nature
Another noteworthy feature of Inca architecture was both their dedication and ability to work with nature and the natural landscape, rather than reshaping their surroundings. While some large-scale restructuring projects were undertaken—the Sapa Inca Huayna Capac famously had the Urubamba River rerouted to build his imperial palace—in many instances, builders and architects adapted their work to their environment rather than the other way around.
One example is the incorporation of large stone outcrops into buildings and structures. In keeping with their precision stone masonry, Inca builders would shape these features to fit seamlessly with their masonry walls, using them as foundations or supports, rather than knocking them down to be replaced with blocks. Not only did the use of these sturdy outcrops provide additional stability in an earthquake-prone area, some scholars suggest a religious element as well. Apus, mountain spirits, played a central role in Inca mythology; interweaving their man-made constructions with these natural elements may have had some spiritual or sacred significance, perhaps in the vein of connecting the human realm with that of the gods.
Another well-known example is the terraces constructed to enable farming on the steep mountains and hillsides of the Andes. Rather than flattening out large swathes of land for agriculture, the Inca carefully built terraces into the existing landforms. Not simply earthen steps, the terraces were reinforced with stone retaining walls, which helped regulate the soil temperature and may have extended the growing season. Builders also altered the soil composition, adding gravel to better conserve water, which was brought down from glaciers via irrigation channels. Perhaps most amazing, though the terracing system was largely abandoned when Spanish colonizers imposed their own farming methods, many of the terraces themselves are still in place today.
Public Works: Roads and Bridges
Large construction projects may be the star of the show when considering Inca architecture, but to truly appreciate their skill, some less showy relics should also be considered: the civil engineering projects that made the empire run. It would have been impossible to administer Tawantinsuyu, which stretched from present-day southwestern Colombia south to just beyond Santiago, Chile, and from the Pacific coast eastward into what are today parts of Bolivia and Argentina, without an efficient system to deliver goods, transport armies, cultivate crops and govern up to 12 million people.
Absolutely essential to its imperial management was the Qhapaq Ñan, a road network covering over 18,000 miles. It consisted of two long main roads, one running along the coast and the other from north to south through the Andes, with many branches running through varying terrain, including coastal lands, jungles, and mountains. The roads were built in keeping with the local terrain, with sections elevated over marshy areas, steps incorporated to traverse slopes, and drainage channels added to ensure excess water would not compromise their stability. Scholars have identified eight road typologies used for the Qhapaq Ñan, demonstrating the skill and innovation employed by the Inca to construct a transportation network that still exists in various places throughout the region today.
Tawantinsuyu was also crisscrossed by a network of rivers and their tributaries, so the great road system also had to incorporate bridges. While elevated platforms were sometimes built over small streams, to cross rivers and gorges, the Inca devised a unique construction that Europe wouldn’t begin using for another 300 years: the suspension bridge.
While not as long-lasting as their stone palaces and temples—though at least one remains today, periodically rebuilt by local communities—these bridges made use of local materials, twisting ichu grass and reeds into thin ropes, which are then braided together to form large ropes strong enough to suspend a floor of woven sticks and grass over distances of up to 150 feet. Modern testing has revealed that the remaining Q’eswachaka Bridge could support up to 16,000 pounds. It may seem curious that a civilization renowned for constructing impossibly sturdy buildings would create such fragile bridges. However, this came in handy during the war against the Spanish invaders: bridges could be disconnected, burned, or otherwise quickly dismantled to impede the colonizers.
