NAVONA Before the genius of Valadier moulded the isolated buildings and waste spaces of the Piazza del Popolo into a noble symmetry, the Navona was considered the finest and most important piazza in Rome. In length and breadth it is a reproduction of the stadium of Domitian, for the houses, churches, and palaces which line the Piazza Navona are based squarely upon the seats and corridors of that old Roman playground. This part of the city, not far from the Pantheon or old Baths of Agrippa, is low, and it has always been easy to flood it with water. The ancient Romans were so keen for shows of every kind that when the great Flavian amphitheatre (the Coliseum) was closed for repairs, Domitian found it necessary to provide a second place of amusement where the gladiatorial combats and the _naumachiæ_ or sea fights could go on without interruption. It was a rule strictly enforced under the empire that no one could open new baths in the city without providing a fresh supply of water. Something more than a century after Domitian, Alexander Severus--having brought the Acqua Alessandrina to Rome--was able to repair Domitian’s old stadium and to use it once more for the _naumachiæ_. In modern times there does not appear to have been any fountain here until the pontificate of Gregory XIII, and at that time the passion for fountain-building in modern Rome really began. Pius IV, the Pope last but one preceding Gregory XIII, had repaired the old aqueduct of the Acqua Virgo, originally brought to the city by Marcus Agrippa, the son-in-law of Augustus, so that that water, which for a long time had been running only intermittently in the fountain of Trevi, could now be obtained in a continuous stream. It is impossible to throw Virgo Water to any great height, and the fountains of the Piazza Navona have had to be constructed with reference to this limitation. [Illustration: The Fountain of the Four Rivers.]