The Agricultural Terraces (Andenes) of the Incas
The agricultural terraces, or andenes, of the Incas were level platforms cut into steep mountain slopes and supported by stone retaining walls, designed to convert marginal land into productive agricultural fields. The Inca built more than 1 million hectares of terraces across the empire, particularly in the highlands of Peru, Bolivia, and Ecuador, and the surviving remains of the system are still in use in many parts of the Sacred Valley of the Urubamba. The terraces are built in a layered form, with a retaining wall, a drainage layer, a moisture-retaining layer, and a top layer of cultivated soil, and the system is one of the most distinctive features of the imperial Inca landscape.
Construction and the layered structure
Inca terraces were built in a sequence of well-defined layers. The retaining wall, which formed the outer face of the terrace, was built of polygonal stones, fitted together with the same dry-stone techniques used in the imperial buildings of Cusco and Machu Picchu. The wall was typically inclined slightly inward, or “battered,” to give it additional stability, and the top of the wall was often capped with a line of larger, more carefully cut stones. The retaining wall was followed by a layer of large stones, the piedra brava, which provided drainage and prevented the upper layers from being washed down the slope.
Above the piedra brava was a layer of q’illpa stones, which were typically of volcanic or glacial origin. The q’illpa layer retained moisture and released it slowly to the upper soil layer, and it is one of the distinctive features of Inca terrace construction. The q’illpa layer was followed by a layer of sandy soil, and finally by a top layer of cultivated soil, which was enriched with the deliberate incorporation of gravel, organic matter, and the remains of previous crops. The total thickness of the layers could be more than 2 meters in the larger terraces, with the piedra brava layer alone accounting for more than a meter of the total.
The layered structure of the terraces had several advantages. The piedra brava layer provided drainage and prevented waterlogging, the q’illpa layer retained moisture and released it slowly to the plants, and the sandy soil layer provided a transition between the moisture-retaining layer and the cultivated soil. The system was highly efficient in its use of water and was well suited to the arid conditions of much of the Andean highlands. Modern soil studies, including work at Moray and at Pisac, have shown that the layered structure could support intensive cultivation for many decades without significant loss of fertility.
Types of terraces
The Inca built several distinct types of terrace, each suited to a different environmental context. The simplest were field terraces for level ground, which were built by raising the level of a flat field above the surrounding terrain. These terraces were used in the valleys and basins of the highlands, where the soil was deep and the water supply was reliable. The second type was the sloped or inclined terrace, used on gentle slopes where the ground was relatively stable. The third type was the steeply walled or pisqa terrace, used on near-vertical slopes where the retaining wall had to support the weight of the entire terrace. The pisqa terrace is the most characteristic of the imperial Inca style and is found throughout the Sacred Valley and at Machu Picchu.
The height of the retaining wall varied with the slope of the ground and the intended use of the terrace. The walls of the terraces of Pisac, on the slopes above the town of Pisac, reach more than 6 meters in the highest cases, while the walls of the terraces of the Sacred Valley floor are typically between 1 and 3 meters high. The width of the terraces also varied, with the wider terraces (up to 10 meters or more) used for the cultivation of maize and the narrower terraces used for potatoes and other tubers.
Pisac and Chinchero
The terraces of Pisac are among the most extensive in the Sacred Valley. The site includes more than 30 levels of terraces, built on a steep mountainside above the town of Pisac, and the terraces are still in use, producing maize, potatoes, quinoa, and a range of other crops. The terraces are integrated with a sophisticated system of irrigation canals that bring water from the upper slopes of the mountain to the agricultural land, and the system is one of the most complete in the region.
The terraces of Chinchero, on the plateau above the town of Chinchero, are also extensive and are still in use. The terraces are built in the standard imperial form, with a polygonal retaining wall, a layer of piedra brava, a layer of q’illpa, and a top layer of cultivated soil. The Chinchero terraces are part of an integrated system that includes irrigation canals, the so-called labyrinth terrace, and a series of ritual structures. The site is one of the most visited in the region and is a popular destination for tourists traveling between Cusco and the Sacred Valley.
The terraces of Ollantaytambo, on the valley floor below the Inca site, are also extensive and are still in use. The terraces are built on both sides of the lower town, and they are integrated with a system of irrigation canals that bring water from the Patakancha River. The terraces are constructed in the standard imperial form, with a polygonal retaining wall and the typical layered structure, and they produce enough food to support the local population.
Moray and the agricultural laboratory
Moray, a few kilometers from the town of Maras, is a unique group of four circular depressions, each of which contains concentric circular terraces. The depressions are natural, but the Inca built the circular terraces to a depth of more than 30 meters in the largest case. The temperature difference between the top and bottom of the largest depression can be as much as 4 to 5°C, and the various terraces create a range of microclimates that simulate conditions at different altitudes in the Andean region.
The Moray site is conventionally interpreted as an agricultural laboratory, in which the Inca experimented with the cultivation of different crops at different altitudes and in different microclimates. The circular form of the terraces, with the highest terraces representing the conditions of the high puna and the lowest representing the conditions of the lowland valleys, allowed the Inca to test the performance of crops under a wide range of conditions within a single site. The interpretation is supported by the presence of irrigation channels that bring water from a natural spring to each of the terraces, and by the presence of small platforms and buildings that are interpreted as observation posts.
The Moray terraces were not used for the large-scale production of food, but they were an important part of the imperial agricultural system. The Inca were keen experimenters with new crops and new techniques, and the mit’a system provided the labor necessary for the construction and maintenance of the Moray terraces. The site is one of the most photographed Inca monuments in the region and is recognized as a National Historic Landmark of Peru.