We know quite a lot about the ancient Roman Empire. Two thousand years ago, the Romans spread their culture to the edge of the continent and beyond, bringing with them philosophy, religion, and a strict government. Roman territories were fertile ground for invention and the arts; unfortunately, researchers now say, they were also fertile ground for parasites.

The Romans’ obsession with cleanliness is legendary. They’ve been credited with the creation of public toilets, heated baths, sewers, plumbing, and even mandatory street cleaning. But in a paper published today in the journal Parasitology, biological anthropologist Piers Mitchell asserts that some of these inventions may have actually made things less sanitary. 

Mitchell reviewed dozens of journal articles on paleoparasitology (the study of ancient parasites) in order to look at the prevalence of parasites before and during the Roman Empire. He compiled data on the presence of 17 different species: 12 internal parasites, such as dysentery, and 5 external parasites, such as lice. The authors of the articles used for the research had collected evidence from ancient latrines, fabrics, and combs. They also sampled coprolites—fossilized poop—and examined Roman-era skeletons for signs of parasite infection. 

Analyzing the journal articles revealed a surprising trend: People in the Roman Empire were riddled with parasites. Infection with tapeworms, whipworm, roundworm, fleas, and lice actually increased during Roman times. 

How could this happen in such a squeaky-clean society? For starters, says Mitchell, the baths probably weren’t helping. Everybody was sharing the same water, which was not changed nearly as often as we’d like to imagine. A scum of human filth and cosmetics would build up on the warm water’s surface, creating a perfect breeding ground for little nasties. 

Then there was the mandatory street cleaning. In theory, getting muck off public roads sounds great. But like so many government projects, it may have had unintended consequences. "It is possible that sanitation laws requiring the removal of faeces from the streets actually led to reinfection of the population as the waste was often used to fertilise crops planted in farms surrounding the towns," Mitchell said in a press release

A Roman whipworm egg found in Turkey. Image credit: Piers Mitchell

The last potential culprit had nothing to do with misguided sanitation efforts. It was a condiment. The fish sauce called garum was the ketchup of the Roman Empire. Unfortunately, with fish comes fish parasites. Mitchell was surprised to find a spike in fish tapeworm infections until he considered garum. Kept at room temperature, the sauce was a natural vector for tapeworm eggs, and there were garum factories and vendors all over the place. Everyone was eating it; as a result, everyone had tapeworms. Okay, not everyone. But a lot of people.

“This appears to be a good example of the negative health consequences of conquering an empire," Mitchell said in the press release.

The prevalence of both intestinal parasites and ectoparasites such as lice suggests that Roman toilets, sewers, baths, and sanitation laws had no clear benefit to public health, Mitchell said. However, he noted that it "seems likely that while Roman sanitation may not have made people any healthier, they would probably have smelt better."