Obelisk Considered to be the Horologium Augusti in Rome, July 2012

Obeliscus Augusti

Samuel Ball Platner (as completed and revised by Thomas Ashby):
A Topographical Dictionary of Ancient Rome,
London: Oxford University Press, 1929.


Obeliscus Augusti, gnomon: an obelisk erected at Heliopolis in the seventh century B.C. by Psammetichus II, brought to Rome by Augustus in 10 B.C. and set up in campus Martius between the ara Pacis Augustae and the columna Antonini Pii (CIL VI.702; Amm. Marcell. XVII.4.12; Strabo XVII.805; Plin. NH XXXVI.71). It is of red granite, 21.79 metres high (cf. Plin. loc. cit.; Notit. Brev.: Jord. II.187), and covered with hieroglyphics (BC 1896, 273‑283 = Ob. Eg. 104‑114). It was standing in the eighth century (Eins. 2.5; 4.3), but was thrown down and broken at some unknown date (BC 1917, 23), and not discovered until 1512 (PBS II.3). It was excavated in 1748, but, in spite of various attempts (LS IV.151), it was not set up again in the Piazza di Montecitorio, its present site, until 1789 (BC 1914, 381). It was repaired with fragments from the columna Antonini.a

Augustus dedicated this obelisk to the Sun (CIL VI.702) and made it the gnomon, or needle, of a great meridian1 (horologium, solarium) p367formed by laying an extensive pavement of marble on the north side of the shaft, the lines indicating midday at the various seasons of the year (Lumisden, Remarks on the Antiquities of Rome, 262; JRS 1921, 265, 266, is wrong), being marked by strips of gilt metal inlaid in the marble (Plin. NH XXXVI.72; Richter 252‑253, fig. 26). Seventy years later the indications of the dial were incorrect, and it was supposed that the obelisk had been slightly displaced by an earthquakeb (Plin. NH XXXVI.73). About 1484, and at various times in the next century, portions of the pavement were found, with the gilt lines, and figures in mosaic around the edge representing the winds and different heavenly bodies, but they were covered up again and are not visible (LS I.83, 136, 169; HJ 611, n26, and literature there cited). The height of the obelisk would require a pavement extending about 110 metres east and west, and 60 north and southc (HJ 610‑612; LR 466‑468; CIL VI.29820).


Text from: penelope.uchicago.edu/Thayer/E/Gazetteer/Places/Europe/It...