Better known as the “fontanone del Gianicolo” (big fountain on the Janiculum Hill), the large fountain of the Acqua Paola was built between 1608 and 1612 by pope Paul the Fifth Borghese (1605-1621) to celebrate the restoration wanted by him of the ancient Trajan aqueduct, since then renamed Acqua Paola. The work is the result of the collaboration between Giovanni Fontana and Flaminio Ponzio, who inspired themselves very successfully to the fountain of the Acqua Felice built twenty years earlier by Sixtus the Fifth Peretti (1585-1590). The materials for the new construction were largely taken from the Forum Romanum and from the ancient basilica of Saint Peter. In 1690 under pope Alexander the Eighth Ottoboni(1689-1691), Carlo Fontana (1634-1714) referred to the design made by Bernini for the Trevi fountain that was never carried out and transformed the original five ponds into the single large pond visible today and opened the central arch. From 1901 to the nineteen-thirties the water from the “fontanone” fed Rome’s first hydroelectric power plant. A curiosity: there is a mistake in the large beautiful epigraph in the attic, because it specifies that the alsietine aqueduct had been restored, while it actually was the ancient aqua traiana.