Today, it houses the Galleria Nazionale d'Arte Antica, the main national collection of older paintings in Rome.

[2] Carlo Maderno, then at work extending the nave of St Peter's, was commissioned to enclose the Villa Sforza within a vast Renaissance block along the lines of Palazzo Farnese;[3] however, the design quickly evolved into a precedent-setting combination of an urban seat of princely power combined with a garden front that had the nature of a suburban villa with a semi-enclosed garden.

[5] In February 1634, a revised version of Il Sant'Alessio, was performed at the Teatro delle Quattro Fontane, the Cardinal's private opera theater in the Palazzo.

Also at the Palazzo Barberini, he initiated a small natural science museum and botanical garden and his collections attested to his interests in ancient sculpture, numismatics and inscriptions.

On the uppermost floor, Borromini's windows are set in a false perspective that suggests extra depth, a feature that has been copied into the 20th century.

As well as Borromini's false-perspective windows reveals, other influential aspects of Palazzo Barberini that were repeated throughout Europe include the unit of a central two-storey hall backed by an oval salone and the symmetrical wings that extended forward from the main block to create a cour d'honneur.

The salon ceiling is graced by Pietro da Cortona's masterpiece, the Baroque fresco of the Allegory of Divine Providence and Barberini Power.

Hidden in the cellars of the rear part of the building, a Mithraeum was found during the construction work of Villa Savorgnan di Brazzà in 1936, dating probably from the second century AD.