The history of San Andrés can't be understood without that of its surroundings: the Zapotitán valley, one of the most fertile plains in El Salvador, watered by the Sucio River and surrounded by volcanoes. That fertility —enriched again and again by the volcanic ash that covered the region— attracted human populations from very ancient times, long before the Maya city we visit today was raised.
However, living in that valley also meant living under the threat of the volcanoes. At some point in the first millennium of our era —the sources usually place the event between the 3rd and 5th centuries AD— a colossal eruption of the Ilopango volcano occurred (the caldera where the lake of the same name lies today). That eruption, known as the 'Tierra Blanca Joven' event for the layer of white ash it left, covered much of central El Salvador in ash and forced the abandonment of wide areas, which became uninhabitable for a time.
When the ash settled and the soils became fertile again, the populations returned to the valley. On that renewed land began to grow the settlement that, in time, would become San Andrés. The relationship with the volcanoes would mark the whole history of the region: the same force that buried and destroyed was the one that, by fertilizing the fields, made possible the life and flourishing of the cities.
After the valley's recovery, San Andrés grew until becoming, during the Late Classic period (between the years 600 and 900 AD), one of the most important centers of central present-day El Salvador. It came to be the capital of a lordship or chiefdom that dominated the Zapotitán valley and exercised influence over smaller populations of the surroundings, including the small village of Joya de Cerén, located very close by.
At its peak, San Andrés displayed a monumental architecture that reflected its power. The heart of the city was the Acropolis, a large raised complex of platforms, courtyards and pyramidal structures where the elite resided and governed. At the foot of that complex extended a great public plaza, surrounded by mounds and platforms. All this ceremonial and administrative architecture shows that San Andrés was a consolidated center of power, with a hierarchical society and the capacity to mobilize labor and resources.
The city took part in the exchange networks that crossed Mesoamerica. In its material culture and in some architectural features, influences have been identified from both the Maya world and the cultures of central Mexico, which indicates that San Andrés was not an isolated point, but a node within a vast system of commercial and cultural relations. The Zapotitán valley, with its agricultural production and its position, sustained the economy of this lordship.
Like so many other cities of the Maya world, San Andrés did not last forever. Toward the end of the Classic period (around the year 900 AD and the following centuries), the site gradually lost importance and population, in a process that falls within the broader phenomenon known as the 'Maya collapse', when numerous centers of the area ceased to function as cities.
The causes of that decline are multiple and still debated by archaeologists: environmental pressures and resource depletion, droughts, conflicts, political reorganizations and population movements are among the factors usually mentioned. In the case of central El Salvador, one must add the recurring role of volcanic activity, which at different moments affected the region (the Ilopango eruption before, and that of the Loma Caldera volcano that buried Joya de Cerén around the year 600 AD).
What is certain is that, over the centuries, the structures of San Andrés were covered by vegetation and by new layers of earth and ash, until they became mounds that the untrained eye could confuse with simple hillocks. The great Maya city lay dormant beneath the valley, waiting for archaeology to bring it back to light much later.
The lands that were once a great Maya city had, centuries later, a second productive life. During the colonial era, the Zapotitán valley —like much of the region— was integrated into the haciendas devoted to the production of indigo, the blue dye extracted from a plant of the same name. Indigo was, during the 17th and 18th centuries, the province's main export product and one of the great engines of its economy, much in demand in Europe for dyeing fabrics.
On the lands of San Andrés an indigo hacienda was set up, with its 'obraje': the facilities where the plant was processed to obtain the pigment. The process consisted, broadly, of soaking the indigo leaves in water tanks, beating the mixture to oxygenate it and separate the pigment, letting it settle and then drying it in the form of loaves or cakes ready for export. It was hard work, which depended on abundant labor.
That colonial obraje was, over time, buried under layers of earth and ash, which helped to preserve it. When the archaeologists worked at the site, they recovered it and today it's displayed protected under a roof inside the park. It's a valuable testimony of a key era of Salvadoran history, and it makes San Andrés a place where two great chapters coexist in the same space: that of the Maya splendor and that of the colonial indigo economy.
Scientific interest in San Andrés began to take shape in the 20th century. Researchers and archaeologists identified that those mounds of the Zapotitán valley hid the structures of an important pre-Hispanic city, and the first excavations began that brought to light the Acropolis, the great plaza and other buildings. Over time, the research allowed the site's chronology to be reconstructed and its role as a regional capital during the Late Classic to be understood.
The archaeological work, added to the conservation of the colonial obraje, led to the decision to protect and open up the place for the public. San Andrés was declared a National Monument and fitted out as an archaeological park, with trails, interpretive signage and a site museum (the Cipactli museum) that displays pieces, models and explanatory panels. Thus, the site went from being a set of dormant ruins to one of the most visited and best-maintained archaeological parks in El Salvador.
Today, San Andrés fulfills a double function: on the one hand, it's a space for the conservation and research of the pre-Hispanic and colonial heritage; on the other, it's a tourist and educational destination that welcomes students, families and travelers. It's worth remembering that a good part of the ancient settlement has still not been excavated: what you see is only a portion of the city, and future research could keep expanding what we know about this lordship of the Zapotitán valley.