Palazzo Nuovo was built in the 17th century under the guidance of Girolamo Rainaldi and his son Carlo. 

Its slanting orientation, which imitates that of Palazzo dei Conservatori opposite, was influenced by a pre-existing retaining wall on the heights of S. Maria in Aracoeli, in the centre of which was a fountain with a statue known as "Marforio", later moved to the courtyard of the Capitoline Museum. 

Externally, the new building is identical to Palazzo dei Conservatori, while the well-conserved decoration of the symmetrically-planned interior features gilded wooden coffering on the first floor.