Why Do People Toss Coins in the Trevi Fountain?

By GovMint :

Tossing coins into the Trevi Fountain is a tradition that is thought to have roots back to old pagan rituals of dropping a coin into a body of water as an offering to deities that resided there in the hope of receiving good luck and fortune.

Today, at the Trevi Fountain, this practice has transformed into a beloved ritual for visitors. According to legend, tossing one coin over your left shoulder with your right hand ensures a return to Rome. Meanwhile, throwing two coins is said to bring love into your life, while three coins are said to pave the way for good fortune, love, AND, marriage in the city. 

Sources Used:

 https://www.romecabs.com/blog/docs/tossing-coin-in-trevi-fountain-myths-rituals/