A study published on Monday in Communications Sustainability suggests that a massive 2,000 square mile canal network in Colombia was built without rulers or top-down command.
The Zenú hydraulic systems
People living in the La Mojana lowlands from the first century BC to the 11th century sculpted their wetland environment by building raised fields, ridges, and canals. These structures are known as the Zenú hydraulic systems, named after the culture that created them.
The network absorbed water during heavy rains and released it during dry seasons. This prevented both flooding and droughts while providing water for plant cultivation and fish access.
Researchers have long debated whether the immense work required elite leaders to direct it, or if it could have been achieved through collective, bottom-up labour.
Mapping the labour
A team of scientists used satellite imagery to map a 1,200-acre patch of the system in unprecedented detail. They built a model to estimate the population and labour costs for that area.
The model assumed about 1,600 people inhabited the area and that half were part of the workforce. Under these conditions, the structures could have been built in under six weeks. This is about half the length of the dry season.
The time required represents a low labour cost that would not have needed top-down organisation to manage.
What the researchers found
Jasmine Vieri, a research associate at the McDonald Institute of Archaeological Research at the University of Cambridge, led the study. She emailed 404 Media to explain the findings.
“La Mojana is a special case study, in that it is the first to demonstrate in concrete, quantitative terms that these massive works are compatible with bottom-up, community-driven organisation,” Vieri said.
She added that the work is part of a broader shift in how archaeology interprets evidence for hierarchy or top-down power.
“As human beings, we tend to understand the world through our own lens, and many of us now live in hierarchical societies, where large-scale infrastructure, monumental architecture, or luxury goods are often commissioned by, or concentrated in the hands of a few,” she continued.
“Archaeological evidence from other regions and periods keeps revealing cases where people came together to achieve ambitious, collective goals through cooperation rather than coercion.”
Tools and scale
The team’s sample included roughly 1,600 ridges and 63 housing platforms. Most were about 4.5-feet tall when initially constructed.
Exact construction dates are unclear. The systems were built before metal tools, such as shovels, emerged. They may have used wood tools instead.
Based on this technology and workforce numbers, the team estimated the largest raised ridge in the sample would have taken a family five months to complete. This ridge stretches for a third of a mile.
A workforce of 800 could have built it in a matter of hours. Some smaller ridge structures could have been built by a single family over a few days.
The results suggest the whole system in this sample could have been renewed once a generation. Just a few days of annual work would have been required.
Surprise at the numbers
“We entered the project with an open mind, although we did consider collective labour one feasible model from the start,” Vieri said.
“However, when we did obtain the estimates, even we were surprised at how low they were, running through them several times just to confirm they were correct.”
The study was co-authored by Fernando Montejo Gaitán of the Colombian Institute of Anthropology and History. He has spent decades researching these ancient waterways. He is part of REVERSEACTION, a project funded by the European Research Council focused on complex technologies in stateless societies.
A strategy for the future
Understanding how these people built such massive works is not just about reconstructing the past. It is also an adaptation strategy for the future, according to the study.
“Instead of focusing on futile attempts at blocking water, policymakers should consider borrowing the pre-Hispanic solution of working with the inundation rather than against it,” Vieri said.
Modern dikes built by the Colombian government are intended to prevent seasonal flooding. They are often breached by high-volume currents, destroying human lives and livelihoods.
In contrast, the pre-Hispanic raised fields functioned to redistribute the flow of water. This enabled human settlement and cultivation above the water level throughout the wet season.
Raised fields simultaneously buffer against severe droughts by storing and gradually releasing water during the drier months.
For more than a millennium, people in this region used this strategy to go with the flow, without the need for top-down direction.
Hopefully, future work might uncover more insights about the role of social organisation in massive works. It is possible that large structures might have emerged from small collectives.
“Answering these questions would contribute much to broader archaeological debates on the relationship between infrastructural scales and political organisation,” Vieri said.
In fact, a key outcome of the research is an open-source pipeline. It can be readily applied to the study of agricultural systems in other regions. This enables cross-comparative research into testing the strength of the evidence for bottom-up, multi-scalar, or top-down social organisation across different time periods or communities.
