Tradition says that if a coin is tossed into the fountain, you are guaranteed to return to the Eternal City. Many visitors make a wish as they throw the coin into the centuries-old landmark.
Of course the wishes can't be revealed to anyone if they are to become true - so who knows what British Prime Minister Boris Johnson, French President Emmanuel Macron, outgoing German Chancellor Angela Merkel wished for.
The tradition also says coins should be thrown by the right hand over the left shoulder - guidelines all but one of the G20 delegates followed.
Draghi was the only one not to throw a coin into the fountain - perhaps because he doesn't need a folklore to guarantee being in Rome.
About a million euros ($1.35 million) worth of coins are thrown into the basin by tourists each year.
All the money goes to a charity that helps the city’s needy.After the coin toss, leaders mingled among themselves and admired the beauty of the fountain, which covers the entire facade of Rome's Palazzo Poli with its allegorical statues of Tritons guiding the shell chariot of the god Oceanus illustrating the theme of the taming of the waters.
The Trevi Fountain is where the late director Federico Fellini set one of the most famous scenes of modern cinema in the 1960 classic film "La Dolce Vita", where Anita Ekberg famously waded in the fountain after midnight, beckoning Marcello Mastroianni to join her.