10 Times Humanity Found the Answer (and Then Forgot)

These second-century Roman latrines had water running beneath them to wash away waste. Prisma/UIG via Getty Images

Joining the Roman Empire, even at the point of a sword, brought with it certain perks. No question, the Romans were groundbreaking engineers, and they often turned that genius to the art of moving, storing and utilizing water. Via aqueducts, underground passages and cisterns, they conveyed water over vast distances, watered fields, fed fountains and, in a sense, flushed their toilets.

When not using the loo at home, Romans did their business using large public latrines, in full view of one another. Within them, beneath rows of marble thrones, channels of running water swept waste into the sewers. But because the Romans lacked both toilet paper and a theory of bacteria, all was not flush with success. In fact, Roman latrines and baths retain signs of many of the diseases and parasites that their hygiene methods ought to have washed away. One explanation: After "bombing at the forum," the Romans passed around a shared sponge on a stick to clean their "Appian Way" — not the most hygienic option. But it's also likely that they didn't change their baths' water often enough, and that the night soil (human poop) with which they fertilized their crops might have brought parasites back in via the food supply [sources: Beck, Smithsonian, Suddath, Wenz].

The Romans didn't invent plumbing, nor did it disappear when Rome fell. Rather, through them it reached an apex to which, after Rome's fall, Europe would not draw near for another millennium [source: Suddath].