In the center of the piazza is a fountain, the
Fontana del Pantheon, surmounted by an Egyptian obelisk. The fountain was constructed by
Giacomo della Porta under
Pope Gregory XIII in 1575, and the
Pantheon obelisk was added to it in 1711 under
Pope Clement XI. The
Aqua Virgo, one of the eleven aqueducts that supplied ancient Rome with drinking water, served the area of the Campus Martius, but had fallen into disrepair and disuse by the late Middle Ages. It was reconstructed under
Pope Nicholas V and consecrated in 1453 as the
Acqua Vergine. In 1570,
Giacomo della Porta was commissioned under
Pope Gregory XIII to oversee a major project to extend the distribution of water from the Vergine to eighteen new public fountains. Construction of the fountain in the Piazza della Rotonda was authorized on September 25, together with a fountain for
Piazza Colonna, and two more for
Piazza Navona; the fountain for the Rotonda, completed in 1575, was of a chalice-type design, around 3.5 to 4 meters in height, and fed with the Vergine water through a
terracotta conduit. Della Porta designed the fountain, and Leonardo Sormani executed it. Due to the slope of the piazza, the fountain is approached by five steps on the south side, and only two on the north. Under the pontificate of
Alexander VII Chigi, projects were set afoot to systematize the piazza and its setting, grading and enlarging it and widening the incident streets, in which
Gian Lorenzo Bernini participated. An engraving by
Giovanni Battista Falda records the work that had been completed at the time of Alexander's death in 1667. In 1711, the fountain was given its current appearance when
Pope Clement XI had the
Late Baroque sculptor
Filippo Barigioni top it with a 20-foot red marble Egyptian
obelisk. The obelisk, originally constructed by Pharaoh
Ramses II for the Temple of
Ra in
Heliopolis, had been brought to Rome in ancient times where it was reused in the
Iseum Campense, a shrine to the Egyptian god
Isis that stood to the southeast of the Pantheon. In the mid-15th century, the obelisk had been erected in the small
Piazza di San Macuto some 200 meters east of the Pantheon, where it remained until its 1711 move to the Piazza della Rotonda. It is still called the
Obelisco Macuteo after its previous location. ==See also==