Prior to the 1830s, Parisians got rid of their waste like residents of most other big cities -- they either threw it holes beneath their homes or tossed it right into the street. Human waste, animal waste and food scraps would mix with the mud in a putrid brew that would fester and breed disease until a strong enough rain came to wash it away. In the Middle Ages, up to a quarter of Europe's population was killed by diseases linked to poor hygiene.

After a particularly bad cholera outbreak, the leaders of Paris ordered the construction of a citywide sewer system. Though modeled on the sewers of ancient Rome, the Parisian sewer was much larger in scale. It contained walkways on either side of the main channel and was tall enough for workers to stand upright. By 1870, over 300 miles had been constructed, making it one of the first large-scale modern sewers, according to sewer historian Jon Schladweiler.

The project was so big it captivated the locals, who insisted on taking boat tours to see just how their money was being spent. "They'd put on their Sunday best and float down the channel with all the sewage," said Schladweiler.