The obelisk that stands in the centre of St Peter's Square is the only one of the city's thirteen ancient obelisks to have remained standing following the fall of Rome at the end of the 5th century.
The obelisk has no hieroglyphs, which makes it difficult to assess its exact age. It was brought to Rome by the Emperor Caligula (r. 37-41 CE) and set up on the spina of the circus he was building on Mons Vaticanus. The circus was completed by Caligula's successor, Nero, and bore his name Circus Neronianus.
For centuries St Peter's Needle, as the obelisk had come to be known by pilgrims, stood on the south side of St. Peter's Basilica. Pope Sixtus V (r. 1585-90) entrusted the task of moving it to the architect and engineer, Domenico Fontana (1543-1607). The obelisk, which is 25 metres high and weighs roughly 330 tons, was erected (with the aid of 900 men, 140 horses and 44 winches) on September 10th, 1586.
The obelisk was originally capped with a bronze globe, which was believed to contain the ashes of Julius Caesar. However, when the globe was opened it was found to be empty. It is now on display in the Museii Capitolini.
At the base of the obelisk sit four bronze lions (each of which has two bodies), whose tails are intertwined.