Horologium of Augustus-Where

 The Horologium of Augustus was a large sundial that was 160 x 75 meters. It was erected by Augustus in the Campus Martius, and served as a clock and a calendar. The gnomon (the part that casts the shadow) was imported from Egypt. It was the first to be brought to Rome. It now stands in the Piazza del Montecitorio. Pliny the Elder stated that, decades after its building, the clock no longer worked, as it was out of alignment.

Picture: http://darkwing.uoregon.edu/~klio/solarium/horologium_augusti.jpg