Architecture Around the World
The early history of the church is inextricably bound up with the great ancient Roman athletics stadium which used to occupy the area of the present piazza, and which has left remains in the crypt.
The Stadium Domitiani was built by the emperor Domitian in the year 86 for athletics competitions in the Greek style, of which he was a fan. Unlike modern athletics stadiums, this one was shaped like an extended horseshoe with the start and end of running races at the southern, straight end.
The structure was massive, and was constructed in brick and limestone. The cavea or terraces for the spectators (10 600 could be accommodated) were in tiers, supported by massive arched vaults with the outer walls faced in travertine. There was much sculptural decoration,
The stadium was also known as the Campus or Circus Agonalis. This comes from the Greek word αγων (agōn), which means a competition involving some effort, usually physical. Hence, it came to mean an athletics meeting, and gave the name agone to the church. (The latter has nothing to do with the English word "agony", which is derivative.) Campus Agonalis mutated over the centuries into navona.
The stadium had a long history. It survived as an open space all the way through the Middle Ages, and in fact was one of the few that the mediaeval city had. Until 1477, when the city's main market was moved to here from the foot of the Capitoline, it continued to be used for sports and games. Only in the 15th century did the old cavea get quarried away completely and be replaced by domestic buildings.
- Wiki: Churches of Rome (online April 2013)
In ancient Rome, what is now the Piazza Navona served as the field of Domitian's stadium for Greek foot races, circa A.D. 86. The area was also periodically flooded in order to stage re-enactments of sea battles, similar to those performed in the colosseum. Throughout the centuries the Piazza was used for festivals, various other athletic events, and as an open air market.
When Pope Innocent X came to power in the 17th century, he decided to transform the Piazza into a showcase for his family, the Pamphili's. To accomplish this aim, he hired Francesco Borromini, Bernini's rival at the time, to construct a new facade for the family's palace, to rebuild the church of Sant Agnese as a family chapel, and to enhance the Piazza's water supply. Bernini's initial role in ornamenting the Piazza was thus non-existent.
In decorating the Piazza, Innocent X decided he also wanted to construct a fountain. This desire was partly logistical and partly personal. For one thing, a new conduit was needed to solve the as yet unresolved problem of where the water from the Vergine aqueduct (that fed the Trevi fountain) was to terminate.
- Art History Presentation Archive (online April 2013)
Pope Innocent X commissioned many of the piazza's landmarks in honor of his family whose mansion stood at the southwest end (now the Brazilian embassy). The most famous of these landmarks, at the piazza's center is the Fountain of the Four Rivers, designed in 1651 by Bernini (who won the commission by bribing the Pope's highly influential sister-in law with a silver model of his proposed work).
At the piazza's south end is the Fountain of the Moor and at the north end is the 19th century Fountain of Neptune. At the mid west side, facing the Fountain of the Four Rivers, is the pope's family church, St. Agnese in Agone.