Scientists have also found ectoparasites, or parasites that live outside the body—lice, fleas, and bed bugs—suggesting the Romans’ bathhouses weren’t keeping them much cleaner than people who lived in Viking or medieval times, who also had lice, but no public baths. Archaeologists have excavated fine-toothed combs from the Roman period, presumed to be for removing lice.

Mitchell speculates that perhaps the steamy bathhouses made a good environment for parasites to grow. “In some baths the water was only changed intermittently, and could acquire a scum on the surface from human dirt and cosmetics,” he writes. The parasites also could have benefitted from the Roman practice of fertilizing crops with human poop. This is still done today in some places, and it is good for the plants … if you first compost the poop long enough to kill off any parasite eggs. But the Romans didn’t know that.

The ancient Romans’ sanitation structures may not actually have been that sanitary, at least by our modern standards, says Ann Olga Koloski-Ostrow, a professor of classical studies at Brandeis University who has been visiting and studying Roman sewers and latrines for more than 40 years.

“In my explorations of public toilets, I have concluded that they must have been pretty dirty places—excrement and urine on the seats and floor, poor lighting … Surely, not someplace one would want to spend much time,” she wrote to me in an email.

Koloski-Ostrow noted that while the toilets didn’t necessarily have a negative effect on public health, researchers should be careful about saying they had a positive effect.

“While the arrival of public latrines in Roman Italy probably did improve the sanitary conditions of cities to some extent, we must not automatically assume that sanitary improvement was the one, the only, or the main Roman motive behind the construction of toilets,” she wrote.

She also suspects that sewers like the Cloaca Maxima were not built with human waste removal in mind, but to help drain standing water from cities.

According to an article she wrote in The Conversation, most people had private toilets at their houses, which weren’t connected to the sewers. “They were afraid of connecting their houses to the sewers, since they feared what might climb out of a sewer into one’s house,” she wrote in her email. (Roman toilet rats!) “They also feared the mephitic gas fires that sometimes burned in sewer holes or in the open seats in public toilets.”

And when they did go to the public latrines, one of the things they used to wipe themselves was a sponge on a stick, which was shared by everybody. Little wonder, then, that the Romans’ toilets—advanced though they may have been—weren’t exactly a public-health revolution.

And in a time when the four humors were the reigning medical philosophy, sound bathroom hygiene may have been too much to expect. In his paper, Mitchell cites Aelius Galenus, who was a physician to Marcus Aurelius and several other Roman emperors. In his writings, Galenus observed and described three different kinds of intestinal worms, but according to Mitchell, he believed that they were created by imbalances in the humors. So if the Romans thought the parasites originated inside the body, rather than outside, there was no reason to link them to sanitation.

“We have no idea what the background thoughts were of the person that invented the toilet,” Mitchell says. “Were toilets invented as a convenient place to put feces, or to cut down on smells, or as a way of stopping you having to walk to the town dump with a pot every morning?” Especially because the Romans didn’t understand how infections work, “you can’t automatically assume that they would have made these sanitation technologies … to make people healthier.”