Piazza Navona, site of the Stadium of Domitian, Rome. Palazzo Pamphilj (Brazilian Embassy), Church Sant'Agnese in Agone, Obelisk of Domitian.

Piazza Navona is a piazza in Rome, Italy. It is built on the site of the Stadium of Domitian, built in 1st century AD, and follows the form of the open space of the stadium. The ancient Romans went there to watch the agones ("games"), and hence it was known as "Circus Agonalis" ("competition arena"). It is believed that over time the name changed to in avone to navone and eventually to navona.
Defined as a public space in the last years of 15th century, when the city market was transferred there from the Campidoglio, Piazza Navona was transformed into a highly significant example of Baroque Roman architecture and art during the pontificate of Innocent X, who reigned from 1644 until 1655, and whose family palace, the Palazzo Pamphili, faced the piazza. It features important sculptural and architectural creations: in the center stands the famous Fontana dei Quattro Fiumi or Fountain of the Four Rivers (1651) by Gian Lorenzo Bernini, topped by the Obelisk of Domitian, brought in pieces from the Circus of Maxentius; the church of Sant'Agnese in Agone by Francesco Borromini, Girolamo Rainaldi, Carlo Rainaldi and others; and the aforementioned Pamphili palace, also by Girolamo Rainaldi, that accommodates the long gallery designed by Borromini and frescoed by Pietro da Cortona.
Piazza Navona has two other fountains. At the southern end is the Fontana del Moro with a basin and four Tritons sculpted by Giacomo della Porta (1575) to which, in 1673, Bernini added a statue of a Moor, or African, wrestling with a dolphin. At the northern end is the Fountain of Neptune (1574) also created by Giacomo della Porta; the statue of Neptune, by Antonio Della Bitta, was added in 1878 to create a balance with La Fontana del Moro.
At the southwest end of the piazza is the ancient 'speaking' statue of Pasquino, erected in 1501. Romans could leave lampoons or derogatory social commentary attached to the statue.
During its history, the piazza has hosted theatrical events and other ephemeral activities. From 1652 until 1866, when the festival was suppressed, it was flooded on every Saturday and Sunday in August in elaborate celebrations of the Pamphilj family. The pavement level was raised in the 19th century, and in 1869 the market was moved to the nearby Campo de' Fiori. A Christmas market is held in the piazza.

Palazzo Pamphilj, also spelled Palazzo Pamphili, is a palace facing onto the Piazza Navona in Rome. It was built between 1644 and 1650.
Since 1920 the palace has housed the Brazilian Embassy in Italy, and in 1964 it became the property of the Federative Republic of Brazil.

more on https://en.wikipedia.org/wiki/Piazza_Navona , http://blog-aus-rom.com/2013/12/21/stadion-des-domitian/