The 'Solare' obelisk (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 1792 and 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 arms of the Braschi family, to which the pope belonged.