The Piscina Mirabilis is the largest ancient Roman freshwater cistern ever built, located in Bacoli near Naples, within the Phlegraean. Is one of the most impressive examples of Roman hydraulic engineering from the Augustan Period (late 1st century BC / early 1st century AD). Often called the ‘Water Cathedral’ or described as a ‘Subterranean Cathedral’, it served as the terminal reservoir for the Aqua Augusta (Serino Aqueduct), a sophisticated 100km-long system.
Measuring 72m in length, 25m in width, and 15m in height, the reservoir has a capacity of approximately 12,600 cubic meters. This massive reserve ensured that the Classis Misenensis—the most important fleet of the Imperial Roman Navy based in the nearby Port of Misenum—remained self-sufficient even during droughts or prolonged sieges.
The structure is carved directly into the tuff rock and features 48 massive cruciform pillars arranged in four rows of twelve. These pillars support barrel-vaulted ceilings that divide the space into five majestic naves. To ensure the structure was perfectly watertight, the walls and pillars were coated with opus signinum (cocciopesto), a specialized and highly durable Roman waterproof mortar.
