In 1600 urbanization, new streets, churches and fountains caused the rione Trevi to be quite crowded, and it did not change significantly 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.

This changed completely the appearance of the higher part of the rione, that was not very crowded but full of small streets, churches and monumental buildings.

Eastward, the rione borders with Sallustiano (R. XVII), from which is separated by Via Leonida Bissolati, Via Giosuè Carducci, Via di Santa Susanna and Largo di Santa Susanna, and with Castro Pretorio (R. XVIII), from which is separated by Piazza San Bernardo and Via XX Settembre.

To the south, the rione borders with Monti (R. I), from which is separated by the Foro Traiano, Via IV Novembre, Largo Magnanapoli, Via XXIV Maggio and Via del Quirinale.