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 the 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.
Augustus dedicated this obelisk to the Sun (
CIL vi. 702) and made it
the gnomon, or needle, of a great meridian
1 (horologium, solarium) formed
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 earthquake (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,
n. 26, and literature there cited). The height of the obelisk would require
a pavement extending about 110 metres east and west, and 60 north
and south (HJ 601-612; LR 466-468;
CIL vi. 29820).
