Emperor Augustus commissioned this massively ambitious project in the first century. He intended the water system to provide drinking water for the Roman colony of Firmum Picenum (now Fermo) on Italy’s Adriatic coast. The water was collected from natural springs and rain, and deep under the city’s tufa rock, the engineers built a complex arrangement of graded cisterns and aeration to purify and store the precious resource. Some historians believe the system was also used to provision Roman expeditionary ships in the nearby harbor of Porto San Giorgio.

When the Roman era ended, the subterranean cisterns fell into disuse, becoming a dumping ground for Fermo’s war-weary citizens. In the 13 century, they got a second life when Dominican monks stumbled upon the underground caverns while building a new monastery. Ever practical, the monks used part of this system for their cellar, and you can still see the stairway and chutes they built from their monastery to store wines.