Moray: The Inca Agricultural Laboratory
Moray is a unique Inca site located in a high-altitude basin approximately 7 kilometers northwest of the town of Maras and approximately 50 kilometers northwest of Cusco, in the eastern Andes of Peru, at an elevation of approximately 3,500 meters. The site consists of four circular depressions, each of which contains concentric circular terraces that descend in a series of platforms to a maximum depth of approximately 30 meters in the largest case. The depressions are interpreted as natural sinkholes, and the Inca built the circular terraces on their inner slopes and integrated them with an elaborate system of irrigation canals and storage buildings. The 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, and it is one of the most photographed Inca monuments in the Sacred Valley of the Urubamba. The agricultural-laboratory reading is widely accepted but not unanimous: a minority of scholars have argued that the site may have served primarily ceremonial purposes, or that the depressions are at least partly artificial rather than purely natural.
The setting and the depressions
The Moray site lies in a broad, flat basin that is bounded on the west by the high peaks of the Vilcabamba range and on the east by the descent to the Sacred Valley. The basin is a region of relatively arid conditions, with most of the precipitation falling on the surrounding peaks and a smaller amount falling on the basin itself. The site is reached by a road that branches from the principal road between Cusco and the town of Urubamba, and it is one of the most visited archaeological sites in the region.
The four depressions of Moray are not identical in size or in form. The largest, sometimes called the Muyu Urco or the “principal” depression, is approximately 200 meters in diameter and 30 meters in depth, and it contains a series of concentric circular terraces that descend in regular steps to the bottom. The second depression, the Siyay, is smaller, with a diameter of approximately 100 meters and a depth of approximately 15 meters. The third and fourth depressions, the Inti Wayna and the Pukara, are smaller still, with diameters of approximately 50 meters and depths of 10 to 15 meters. Each depression contains a series of concentric circular terraces, and the four depressions are connected by a system of access paths and irrigation channels.
The depressions are natural, formed by a combination of geological subsidence and erosion, and the Inca built the circular terraces on the natural contours of the depressions. The terraces are constructed in the standard imperial form, with a polygonal retaining wall, a layer of large stones for drainage, a layer of q’illpa (volcanic or glacial material) to retain moisture, and a top layer of cultivated soil. The terraces are still visible across the site, although they have been damaged by erosion and by the partial collapse of the retaining walls.
The temperature gradient
The most distinctive feature of Moray is the temperature gradient that exists within the larger depressions. The temperature difference between the top and bottom of the largest depression, the Muyu Urco, 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 temperature at the top of the depression is similar to that of the surrounding plateau, with cool nights and mild days, while the temperature at the bottom is significantly warmer, with mild nights and hot days, similar to the conditions of the lower valleys of the Andes.
The temperature gradient is the result of several factors. The depressions act as thermal reservoirs, absorbing heat during the day and releasing it slowly at night, and the walls of the depressions protect the interior from the cool winds that blow across the plateau. The combination of these factors creates a range of microclimates within the depressions, with the highest terraces representing the conditions of the high puna (above 4,000 meters) and the lowest terraces representing the conditions of the lowland valleys (below 2,000 meters).
The Inca were aware of the temperature gradient and used the different terraces to grow different crops. The highest terraces, with the coolest conditions, were used for potatoes and other tubers, while the lowest terraces, with the warmest conditions, were used for maize and other grains. The middle terraces were used for quinoa, oca, and other crops of intermediate altitude. The system allowed the Inca to test the performance of crops under a wide range of conditions within a single site, and to identify the varieties that were best suited to each altitude.
The irrigation system
The Moray site is integrated with an elaborate system of irrigation canals and channels that bring water from a natural spring to the terraces. The principal canal begins at a spring on the slopes of the Chinchero range, on the western edge of the basin, and runs for approximately 8 kilometers to the site. The canal is built of polygonal stones, with a fine lining of clay or sandy soil, and it is cut into the bedrock in many places. The canal is still in use in some sections, although it has been damaged by erosion and by modern interventions.
The water from the principal canal is distributed to a series of small channels that run along the contours of each terrace, and the channels deliver water to each level of the depressions. The channels are built of polygonal stones, with a sequence of small drops and outlets that distribute the water across the terraces. The system is one of the most elaborate in the imperial Inca record, and it is cited in modern studies of Inca hydraulic engineering as an example of the technical sophistication of the imperial water management.
The irrigation system is also integrated with a sequence of storage buildings on the eastern edge of the site, which are interpreted as qollqas, the standard Inca storehouses. The buildings are built of polygonal stone, with half-buried floors and small doorways, and they are similar in form to the qollqas of Tipón and other imperial sites. The presence of the qollqas at Moray supports the interpretation of the site as a focus of agricultural experimentation, since the storage buildings would have allowed the Inca to preserve the produce of the experimental crops for further study and distribution.