in 508 BC, it is said that the forces of Lars Porsena occupied the Janiculum and laid siege to Rome. The water mills During the third century AD, a complex of water-mills was built here to grind grain to provide bread flour for the city. As revealed by excavations in the 1990s under the present American Academy in Rome, they sat astride the aqueduct Aqua Traiana and were in brick-faced concrete with a cocciopesto floor. In the limited excavated area, two mill races branched obliquely off the Aqua Traiana, turned to run parallel to the aqueduct for some distance, and then turned back to feed into the aqueduct again. It appeared that the northern mill race had 3 or 4 millwheels of 2.30 m diameter and width about 1.65 m to provide a sufficiently large working area, but only 2.6 m between their axle centres which must have reduced efficiency due to turbulence between them. The southern race had one a larger wheel. The site resembles Barbegal, although the excavations show that they were undershot rather than overshot in design (i. e. with the stream entering at the bottom of the wheel, not the top). The mills were still in use in 537, when the Goths besieging the city cut off their water supply, the Aqua Traiana. But they were later restored and may have remained in operation until at least the time of Pope Gregory IV (827–844). The Aurelian Walls were continued up the hill by the emperor Aurelian (reigned AD 270–275) to include the water mills. The mills were already known from observations by R. Lanciani in the 1880s. 19th century to present The Janiculum is the site of a battle in 1849 between the forces of Garibaldi, defending the revolutionary Roman Republic against French forces, who were fighting to restore the temporal power of the Pope over Rome. Several monuments to Garibaldi and to the fallen in the wars of Italian independence are on the Janiculum. Daily at noon, a cannon fires once from the Janiculum in the direction of the Tiber as a time signal. This tradition goes back to December 1847, when the cannon of the Castel Sant'Angelo gave the sign to the surrounding belltowers to start ringing at midday. In 1904, the ritual was transferred to the Janiculum and continued until 1939. On 21 April 1959, popular appeal convinced the Commune of Rome to