Acqua Paola

The Aqua Traiana (later rebuilt and named the Acqua Paola) was a 1st-century Roman aqueduct built by Emperor Trajan and inaugurated on 24 June 109 AD. It channelled water from sources around Lake Bracciano, 40 kilometers (25 mi) north-west of Rome, to Rome in ancient Roman times but had fallen into disuse by the 17th century. It fed a number of water mills on the Janiculum, including a sophisticated mill complex revealed by excavations in the 1990s under the present American Academy in Rome. Some of the Janiculum mills were famously put out of action by the Ostrogoths when they cut the aqueduct in 537 during the first siege of Rome. Belisarius restored the supply of grain by using mills floating in the Tiber. The complex of mills bears parallels with a similar complex at Barbegal in southern Gaul.

Both the ancient Aqua Traiana and the modern Acqua Paola were fed by a collection of aquifer sources in the hills around the volcanic basin of Lake Bracciano. The Italian archaeologist Alberto Cassio in his Route of the Ancient Waters, and his successor Rodolfo Lanciani in 1881 in his Commentary on Frontinus list the sources in the following groups, running clockwise around the lake from Bracciano:

The Architect Carlo Fontana had measured and compared the yield of various of these sources on two occasions in the early 1690s, and documented his measurements in his Really Useful Treatise published in 1695.

The most significant and copious source of the Aqua Traiana is pinpointed by Carlo Fea (1832) as close to the Fosso di Fiora in the modern district of Manziana. Fea makes reference to a document written by the architect Luigi Bernini on 25 February 1667 to Pope Alexander VII Chigi.

The Manziana source has never formed part of the modern Aqua Paola, but, in 1667, Alexander VII wanted to add additional water to the Acqua Paola to power his new fountain in St. Peter's Square. Bernini measured the water at this source as supplying 340 "oncie" of water of perfect goodness and lightness. This water was sufficiently copious, according to his calculation, to double the yield of the Acqua Paola. It supplied as much water as all the rest of the sources put together.

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