On 21st April, Rome's birthday, the sunbeam hits the metal grille above the door and floods the outside courtyard with light. Imagine what the ancient Romans thought when they saw their Emperor bathed in this glow. No wonder they believed Emperors were Gods.
Another sundial can be found in Piazza Montecitorio, behind the parliament buildings.
Originally a solar meridian line was drawn at the foot of the obelisk which demonstrated the accuracy of the calendar introduced by Julius Caesar. A modern meridian line can be found in the paving in Piazza Montecitorio.
If you wish to know the time in the Villa Borghese Gardens you can consult the Water Clock which runs on a hydraulic mechanism. It fits in beautifully within the surroundings, appearing to be almost part of the rocks and foliage. The clock was exhibited at the Paris Expo in 1867
Perhaps my favourite way of telling the time in Rome is to look up to the Torre dell'Orologio in the piazza of the same name. This Borromini designed tower is a delight to behold but is close to my heart as I think of it as the 'Magic of the Movies' clock. It appears outside the window of Joe Bradleys Via Margutta apartment in Roman Holiday, miles away from the real location.