Short answers, pulled from the story.
Emperor Augustus ordered this red granite monument brought to Rome in 10 BC alongside the Flaminio Obelisk. Roman engineers erected it as the gnomon of the Solarium Augusti within the Campus Martius district.
Workers transported the massive stone to the sanctuary of Ra in Heliopolis for final erection while Pharaoh ruled Egypt between 595 and 589 BC. The hieroglyphs on its sides declare it the Golden Horus beautifying the Two Lands.
The new layout of Piazza Montecitorio opened on the 7th of June 1998 establishing current placement for the ancient stone. A fresh meridian line traces toward Palazzo Montecitorio main entrance honoring Augustus original design intent.
By the 40s AD Pliny noted observations no longer agreed due to celestial changes or ground shifts. Earthquakes possibly including one in 849 caused the structure to collapse during the Middle Ages.
The structure measured eighty-five feet plus three-quarters excluding its base according to Pliny the Elder. Sunlight cast shadows that aligned with the Ara Pacis altar on September 23rd each year.