Rome's grandest fountain took 30 years to build, still runs on a 2,000-year-old aqueduct, and hides a small revenge in plain sight. Here's what you're looking at, and what to listen for when you stand in front of it.
On the right side of the fountain sits a large stone vase that looks out of place. The story goes that a barber nearby kept criticising Salvi's work, so the architect added the vase to block his view of it. Romans call it the "ace of cups".
The Trevi is the end of the Aqua Virgo, an aqueduct Agrippa opened in 19 BC. Legend says a young girl showed thirsty Roman soldiers the spring, which is why it's called the "virgin" aqueduct; a relief above the right niche shows her pointing the way.
Visitors throw in around €1.5 million a year. The city collects it and gives it to Caritas, the Catholic charity, which uses it for food programs for people in need.
Tradition says one coin, thrown with your right hand over your left shoulder, means you'll return to Rome. The custom became popular in the 20th century, helped by films like "Three Coins in the Fountain" (1954).
Nicola Salvi won the 1730 design competition and worked on it until his death in 1751; Giuseppe Pannini finished it in 1762. Pietro Bracci sculpted the central figure of Oceanus.
Early morning, before 8 am, when the square is nearly empty.