A city built on water and stone
On the southern slope of the Turrialba Volcano lies Costa Rica's most significant archaeological site, the Guayabo National Monument. The city was occupied for an exceptionally long period, from approximately 1000 BCE to 1400 CE. Its most developed phase, when the major stone structures visible today were built, occurred after 800 CE. At its peak, the settlement may have housed as many as 10,000 people. Yet, for reasons that remain unknown, the inhabitants abandoned the city around 1400 CE, a full century before the arrival of the Spanish.
The excavated portion of the city, which is only a fraction of the total area, reveals a society with sophisticated knowledge of engineering and urban planning. The core of the settlement consists of 43 circular stone mounds, or montículos, which served as foundations for large wooden buildings. These mounds vary in size, with the largest measuring 28 meters in diameter and 2.76 meters in height. A network of stone-paved causeways, called calzadas, connects the mounds and ceremonial areas, with some roadways extending for several kilometers to link surrounding settlements.
The most notable feature is the city's hydraulic engineering. A complex system of open and closed aqueducts and stone-lined channels brought fresh water from nearby springs into the city for distribution and storage in tanks. This system was so well-constructed that parts of the ancient aqueducts still function today. This achievement was recognized in 2009 when the American Society of Civil Engineers designated Guayabo an International Historic Civil Engineering Landmark.
The agroforestry puzzle
The complexity of Guayabo's architecture is an archaeological puzzle. Monumental construction on this scale is typically associated with societies supported by intensive grain-based agriculture, such as the maize cultivation of the Maya and Aztecs. Such farming produces large surpluses that can be stored and used to support a specialized workforce of builders and engineers. At Guayabo, however, there is little evidence of widespread, intensive farming or large-scale food storage facilities.
Instead of vast fields of a single crop, the people of Guayabo likely relied on a mixed economy of agriculture, hunting, and fishing. Their farming practices probably involved a sustainable system of agroforestry, cultivating a variety of plants within the surrounding rainforest. This would have included tree crops, roots, and palms, which do not require clearing large tracts of land. This model of subsistence challenges the conventional theory that urbanism and monumental building depend on the centralized control of grain surpluses. The social organization of Guayabo may have been based not on control over food, but on political and religious leadership.
Throughout the site, archaeologists have uncovered numerous petroglyphs carved into boulders. These designs include geometric shapes and depictions of animals native to the area, such as jaguars, lizards, and birds. One of the most noted carvings features a jaguar on one side and a lizard on the other, possibly representing an important element of the inhabitants' cosmology.