The obelisk is located at 41.902245, 12.457274 in the center of the Square. According to the
Vatican website (http://www.vatican.va/various/basiliche/san_pietro/it/basilica/esterno.htm) the red granite obelisk was is 25.31-meter tall on a base of 8.25 meter. It was originally placed on the axis of the Circus of Nero—or Circus of Caligula.
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| An early interpretation of the relative locations of the circus, and the medieval and current Basilicas of St. Peter. Retrieved from https://en.wikipedia.org/wiki/Circus_of_Nero#/media/File:Plan_of_Circus_Neronis_and_St._Peters.gif |
The obelisk has a square plan aligned to true north and its shadow acts as a sundial. The surrounding pavement made of sampietrino (beveled basalt stones) and has inserted white marble markers defining a wind rose. The wind rose markers were not added until 1852 during the pontificate of Pius IX.
