The water crashing across Trevi Fountain arrives through the Aqua Virgo, an aqueduct that Agrippa's engineers opened in 19 BC and Rome has never let run dry. Nicola Salvi won the commission in 1732 and shaped the theatre you see until his death in 1751; others completed it only in 1762. He built it directly against the front of Palazzo Poli, using the whole palace facade as the fountain's backdrop. At its centre stands Oceanus in a shell chariot, drawn by two sea horses, one rearing and one calm, for the changing temper of the sea.
You hear Trevi before you see it, the roar bouncing off narrow lanes until the square opens and the whole wall pours down in front of you. Water the colour of jade slides over carved reefs into the basin, where the old ritual endures: a coin flicked over the shoulder to promise a return to Rome. Those coins, more than a million euros a year, are scooped out and given to charity. The crowd is constant now and the ledges are off limits, yet the sound and the light on wet stone still hold everyone in place.