Very cool [for others: press the left or right arrow on your keyboard to rotate the view around to see the obelisk in question]
According to the
Encyclopaedia Romana,
“An inscription on the base indicates that Constantine the Great had intended to install the obelisk in his new capitol at Constantinople. It was removed from Karnak, but Constantine died in AD 337 and the obelisk remained in Alexandria until his son Constantius had it transported to Rome instead. The oldest obelisk in Rome and the last to be brought there, it was discovered in 1587, broken in three pieces. The next year, it was reerected in the Piazza di San Giovanni in Laterano by Sixtus V as part of his scheme of urban development.”
According to
a site devoted to Roman art:
“All the obelisks are no longer on the site where they were erected by the Roman Emperors. In the XVIth century most of them were broken into pieces and they were just another component of the picturesque view of the Roman ruins. They were saved by Pope Sixtus V (1585-90) who used them as focal points for some of the new streets he opened as part of his plan of urban development. Several obelisks were repaired, turned from pagan to Christian monuments by the addition of new inscriptions, topped with a cross and with the heraldic symbols of the pope and eventually moved to the center of a piazza or in front of a basilica.”