Short answers, pulled from the story.
The Obelisk of Montecitorio is an ancient Egyptian obelisk made of red granite, originally quarried at Aswan and erected at the sanctuary of Ra in Heliopolis during the reign of Pharaoh Psamtik II, who ruled from 595 to 589 BC. It now stands in the Piazza Montecitorio in Rome.
Emperor Augustus brought the obelisk to Rome in 10 BC to serve as the gnomon of the Solarium Augusti, a giant sundial in the Campus Martius. He also oriented it so its shadow fell on the Ara Pacis on the 23rd of September, his birthday, which coincided with the autumnal equinox.
The obelisk stands 21.79 meters high. Including the base and the globe, the total height is 33.97 meters.
The meridian of the Solarium Augusti was worked out by the mathematician Facondius Novus. The sundial covered a surface of 160 by 75 meters, paved in travertine with bronze letters marking hours, months, seasons, and signs of the zodiac.
The obelisk collapsed sometime between the 9th and 11th centuries, possibly due to fire, earthquake, or war, including the earthquake of 849 or the siege of Rome in 1084 by Robert Guiscard. It then became progressively buried beneath the city.
Pope Pius VI carried out restoration works from 1789 to 1792, with the architect Giovanni Antinori directing the project. Antinori repaired the obelisk using granite taken from the Column of Antoninus Pius.