“Horologium Augusti”

A modern name given to the monumental sundial on the *Campus Martius, which was designed by the mathematician Novius Facundus and constructed by Augustus in 10 B.C. It used one of the two obelisks brought from Heliopolis as its gnomon (cf. *Obeliscus: Circus Maximus), and bronze marks in the pavement measured the seasonal changes in the length of the shadow this cast at midday (Pliny, NH 36.72-73). Remains of this N–S meridian line were discovered in 1979-81, reinstalled in a travertine pavement of Domitianic date (Buchner 1982; id., LTUR). In this apparent recalibration of the device, bronze letters (reused from the original Augustan phase of the monument) denote the Greek months during which the shadow would reach certain marks along a hatched line. The inscription on the obelisk’s base records its connection with Egypt, as well as Augustus’ dedication of the entire monument to Sol (CIL VI 702=ILS 91). The sundial itself seems to have functioned primarily as a large solar calendar. Its full reconstruction is not clear, but as yet there is no hard evidence to suggest the presence of other bronze lines to mark hours of the day other than noon. The question of the sundial’s overall layout is complicated by the presence of Flavian pomerial cippi along a line immediately to the W of the meridian (Rodríguez Almeida). Nevertheless, a plaza of some sort is to be expected, and we can assume that there was a large open space around the obelisk at the time of its dedication. Addendum On the extensive debate over the precise placement and height of the obelisk and its once-visualized connection with the Ara Pacis: Urbem 169 n.220, with p. 273-74 (Addenda).