The meridian, worked out by the mathematician Facondius Novus, was placed in the center of a surface measuring 160 by 75 metres (525 by 246 ft), constructed from slabs of travertine, on which a quadrant was marked out with bronze letters, with indications of the hours, months, seasons and signs of the zodiac.

Besides its function as a solar clock, the obelisk was oriented in such manner so as to cast its shadow on the nearby Ara Pacis on 23 September, Augustus's birthday, which coincided with the autumnal equinox.

This orientation “sanctioned his divine right to rule” and “possibly his right to establish a dynasty.”[citation needed] A detailed description that gives us the typology, appearance and formal operating procedure of this imposing solar meridian is supplied from Pliny the Elder (Naturalis historia 36, 71–72): "The one [obelisk] in the Campus was put to use in a remarkable way by divine Augustus so as to mark the sun’s shadow and thereby the lengths of days" [7] The inscription written on two sides of the obelisk's base runs as follows:

Pope Sixtus V (1520–1590) made some attempts to repair and raise the obelisk, reassembling some pieces that had been found in 1502 in a cellar off the "Largo dell'Impresa", the present Piazza del Parlamento.

After this fruitless attempt, some traces of the meridian were recovered during the pontificate of Benedict XIV in 1748, who found parts of it under the main entrance of Piazza del Parlamento 3, sited just as in Pliny's description.