The Obelisco Solare (21.79 m), which stands in Piazza del Montecitorio, was originally erected by the pharaoh Psammetichus II (r. 595-589 BCE) in Heliopolis. In 10 BCE it was moved to Rome, where it became the gnomon of a huge sundial (Horologium Divi Augusti) in the Campus Martius.
It was unearthed in the 16th century and in 1792 the much-repaired obelisk was erected in Piazza del Montecitorio, at the behest of Pope Pius VI (r. 1775-99). A pointer was also added, as a reminder of its original role as a part of a sundial. The bronze sphere sports the heraldic charges of the coat of arms of the Braschi family, to which the pope belonged.
The inscriptions on the north and south faces of the base date back to the time of Augustus, while the almost unreadable inscriptions on the west and east faces were added at the behest of Pius VI.
The Augustan inscriptions read: IMP CAESAR DIVI F / AVGVSTVS / PONTIFEX MAXIMVS / IMP XII COS XI TRIB POT XIV / AEGVPTO IN POTESTATEM / POPVLI ROMANI REDACTA / SOLI DONVM DEDIT. (Emperor Caesar Augustus, son of the divine Caesar, Pontifex Maximus, acclaimed Consul for the eleventh time and Tribune for the fourteenth time, upon the subjection of Egypt to the power of the Roman people, gave this as a gift to the sun.)
The inscription on the west face reads: PIVS VI PONT MAX / OBELISCVM /REGIS SESOSTRIDIS A C CAESARE AVGVSTO / HORARVM INDICEM / IN CAMPO STATVTVM / QVEM IGNIS VI / ET TEMPORVM VETVSTATE / CORRUPTVM / BENEDICTVS XIIII P M / EX AGGESTA HVMO AMOLITVS / RELIQVERAT / SQVALORE DETERSO / CVLTVQVE ADDITO / VRBI CAELOQVE RESTITVIT / ANNO M DCC XCII / SACRI PRINCIPATVS EIUS XVIII. (Pius VI, Pontifex Maximus, after the removal of dirt and the addition of ornament, restored to the city and to heaven the obelisk of King Sesostris, set up in the campus by Gaius Caesar Augustus as a marker of the hours, and which damaged by fire and the long flight of time, Benedict XIV, Pontifex Maximus, having removed it from the earth, in the year 1792, the eighteenth of his sacred pontificate.)
The inscription on the east face reads: QVAE CELERES OLIM SIGNABAT PYRAMIS HORAS / FRACTA DEHINC LAPSV SPRETA IACEBAT HVMO / ANTIQVVM RENOVATA DECVS NVNC FRONTE SVPERBA / DINVMERAT SEXTI TEMPORA FAVSTA PII. (The pyramid that once marked the swift hours, thereafter lay neglected on the ground, broken in its fall, its former beauty renewed, now with proud appearance, it counts off the happy hours of Pius VI.)