Trevi is the rione II of Rome. The origin of its name is not clear, but the most accepted possibility is that it comes from the Latin trivium (meaning "three streets"), because there were three streets all leading to "piazza dei Crociferi", a square next to the modern Trevi square. Its logo is made of three swords on a red background.

This rione, during the Roman republic belonged to the third region, while during the Roman empire was split up into two regions: the VI, called Alta Semita and the VII, called via Lata.

During the ancient Roman period, in rione Trevi there were large groups of private houses with some monumental buildings. Since that time the area was actually split up into two parts: a lower one, level and next to the river Tiber, and a higher one on the hills. The first one was one of the center of the activities of the city, while the second one was a rich and peaceful residential area.

After the fall of the Roman empire, a lot of people moved away from the hills to settle next to the river, in the lower part. The urbanization followed the people: next to the river Tiber the rione was full of buildings while almost nothing was built again on the hills until the Renaissance.

In 1600 urbanization, new streets, churches and fountains caused the rione Trevi to be quite crowded, and it did not change sensibly until the end of the 19th century. The Quirinal Hill, partially isolated from the crowded part close to the river, was slowly becoming a center of power thanks to numerous buildings belonging to the Pope.