How medieval Trondheim’s waste rules may have spread roundworm

Medieval towns had a reputation for filth, but the story from Trondheim in Norway is more surprising. Researchers say the town’s leaders took active steps to protect public health, yet one well-meant rule likely made people sicker. Moving latrine waste out of town and spreading it on farmland appears to have helped roundworm infect almost the entire population.

A town that took health seriously

The findings come from a book called Health in Medieval Urban Trondheim: From Individual to Communal Responsibility AD 1000-1600, published in August 2026. Archaeologist Axel Christophersen, professor emeritus at the NTNU University Museum, led the research project behind it, known as MedHeal600. Erik Opsahl and James Barrett edited the volume with him.

The big theme is a change in who carried responsibility for health. Early on, households dealt with their own hygiene and waste. Over the Middle Ages, towns increasingly treated these things as a shared duty. Norway’s national law code of 1274 and the town law of 1276 helped frame the role of local communities in the common good.

When a smart idea backfired

Trondheim ordered people to move latrine waste outside the city. That sounds sensible, because it kept the smell and the mess away from homes. But farmers used the waste as manure on their fields. According to PhD researcher Elisabeth Forrestad Swensen, who analysed the contents of medieval latrines, this practice spread roundworm, and the parasite infected nearly the entire population.

The logic is simple. Roundworm eggs leave the body in feces. If people spread that waste on crops, the eggs can end up back on food, and people swallow them again. A system built to clean up the town may therefore have closed a loop of infection.

The role of wood chips

The study also describes a quieter change. Builders left wood chips from construction, and people used them to mask odors in waste pits. In the late 13th century the supply of chips dropped. The researchers suggest this possibly links to climate effects of the 1257 volcanic eruption in Indonesia and to local timber running low, although they treat that explanation with caution.

Without the chips, pits along residential streets became harder to live with. Residents abandoned them and shifted toward carrying organic waste out of the city. That change lowered the infection risk linked to waste sitting in the middle of town, even as the farmland route kept roundworm in circulation.

What the skeletons add

The team also studied skeletons from two Trondheim cemeteries. Well over half of the people showed signs of physiological stress in childhood and adolescence, which points to poor diets during growth. Health and mortality looked worse among people from the poorer craft district than among the elite merchant families who lived in an area called Kaupmannastretet.

Then came the Black Death. It reached Norway in 1349 and, by the researchers’ estimate, killed about one-third of the population. Repeated plague outbreaks followed. Norway’s population likely fell from about 500,000 around 1340 to about 200,000 by the early 16th century.

Why it matters

This work challenges the picture of medieval people as careless about hygiene. Trondheim’s authorities clearly tried to manage waste and water for the common good. The roundworm story shows how hard that job was without modern knowledge of parasites. People did not know that eggs in manure could return through food, so a reasonable fix created a new problem.

Caveats and open questions

Several parts of the account remain tentative. The link between the wood chip decline and the 1257 eruption is a possibility, not a settled fact. Death toll estimates for the Black Death in Norway vary between studies, and other researchers have suggested figures closer to half the population. We also read the findings through a news summary rather than the book chapters, so readers who want the full evidence should consult the book itself.

Even so, medieval Trondheim offers a reminder that good intentions and good science are not the same thing, and that public health has always been a learning process.

Sources

• Opsahl, E., Christophersen, A. and Barrett, J. (eds.), Health in Medieval Urban Trondheim: From Individual to Communal Responsibility AD 1000-1600, Scandinavian University Press, 2026 (as reported by Norwegian SciTech News; book page not verified)
• Norwegian SciTech News (NTNU): The introduction of a medieval public health system exposed the population to roundworm
• Phys.org: The introduction of a medieval public health system exposed the population to roundworm