Piscina Mirabilis is one of the largest drinking water tanks built by ancient Romans. It is located on the west end of the Gulf of Naples, Italy.
This reservoir was intended to supply the Roman fleet – stationed at Portus Julius – with fresh drinking water. The reservoir was 15 meters high, 72 meters long and 25 meters wide. Its area was 1,800 square meters. Water was supplied via Aqua Augusta. The building was based on 48 pillars.