In an epic example of turning lemons into lemonade, the ancient Maya rapidly rebuilt cities destroyed by a catastrophic volcanic eruption, and used the volcano's ash to do it.
Almost 1,500 years ago Central America experienced the Tierra Blanca Joven (TBJ) eruption, the region's greatest eruption since the last Ice Age ended. The blast left a crater lake and a 40-kilometer (25 miles) surrounding area knee-high in ash. The TBJ wiped out nearby Maya cities and sent the civilization as a whole into a temporary decline, known as the Maya Hiatus.
Eventually, the Maya recovered and rebuilt the destroyed cities, but archaeologists have been uncertain as to how long this took. A study published in Antiquity suggests the cities' resurrection came very much at the quicker end of previous speculation, and volcanic ash became an important building material.
The TBJ eruption was so large it probably caused a noticeable cooling throughout the Northern Hemisphere, detected in tree rings and reports of famines. Tephra (fragmentary volcanic material) from the eruption buried the Zapotitán Valley 50 centimeters (20 inches) deep, but dating it has proved difficult, with estimates from 408 to 540 CE.
Uncertainty about the TBJ's timing has contributed to a debate about how long it took for the Maya to recover from such a setback. Some scholars claim the most affected region remained uninhabited for up to two centuries. However, Dr Akira Ichikawa of the University of Colorado, Boulder has challenged this, with evidence public buildings were rebuilt at San Andrés in what is now El Salvador soon after. San Andrés lies in the heart of the valley, 40 kilometers (25 miles) west of the Ilopanga Caldera, the site of the eruption.
The area surrounding San Andrés would have initially been uninhabitable, even for those who survived, but soon after it was settled again the people built the Campana, for a while the largest building in the Valley at 7 meters (23 feet) high and 23,000 cubic meters in volume.
The Campana was a pyramid sitting on top of a flat platform and Ichikawa reports it is constructed partly with the TBJ tephra. The pyramid's top sat 20 meters (66 feet) from the ground.
Although varying architectural styles indicate the Campana was built, or more likely rebuilt, in several stages, according to Ichikawa, “The radiocarbon data suggest that construction began within decades of the TBJ eruption date.” At most, it was 80 years between the eruption and the Campana being built he concludes, and possibly just 30, although this relies on the latest proposed dates for the explosion.
The use of the tephra may have sanctified the Campana in its makers' eyes. “In the Mesoamerican worldview, volcanoes and mountains were recognized as sacred places,” Ichikawa notes in the study. “This work might have had a religious purpose, enabling social integration, as well as creating a sense of community among participants during the difficult times following the eruption.”
Although small compared to the Egyptian pyramids, the task was daunting for the available population. Ichikawa calculates it would have taken more than 150,000 person-days to build the structure. This is almost three years for 1,000 laborers working 60 days a year, assuming survival required most of their time be spent elsewhere.
We don't know if the former inhabitants of the Valley fled the eruption and returned soon after, or if they were wiped out and replaced by immigrants from the east. Ichikawa thinks it is more likely at least some of those who rebuilt San Andrés were the former occupants, or their children based on cultural continuity across the gap.
San Andrés went on to become a primary regional center from around 600-900 CE. The subsequent Loma Caldera eruption was followed by the building of an even larger and more labor-intensive structure in the city, known as the Acropolis.