Bulla Regia
About
Builders at Bulla Regia raised eight massive vaulted cisterns side by side at the edge of town to store water for a wealthy trading city that shipped wheat, olive oil, and exotic circus animals to Rome. The cisterns doubled as a passive cooling system: shafts let attendants sprinkle water down onto the mosaic floors of the town's famous half-underground villas, and the evaporating water pulled the worst of the North African heat out of the rooms below. Bulla Regia's elite built their houses with an entire sunken story specifically to escape the summer sun, something almost no other Roman city bothered to do. The cisterns still stand today as the first structure visitors see walking into the site.
What happened here
Underground, vaulted, and much larger inside than anything visible above suggests. The walls are lined with waterproof mortar, the corners rounded so nothing can lodge, and the roof carried on rows of piers. Water arrives by aqueduct or off the roofs and is held against the dry months, for a fleet, a bath house, a fort or a whole town. Sediment settles in a trap before the main tank, and the tank is drained and scrubbed on a cycle by men who go down by ladder. Access is through shafts with stairs, and it is cool enough down there that things are stored in them. A town on a dry site lives or dies by its cisterns, and they are among the first things built.
Sources
Nearby
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