Piazza Navona is a city square in Rome. 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 came 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, the Piazza Navona was transformed into a highly significant example of Baroque Roman architecture and art during the pontificate of Innocent X, who reigned in from 1644 until 1655 and whose family palace, the Palazzo Pamphili, faced the piazza. 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 here in pieces from the Circus of Maxentius.