The original building was built in 1630 instead of a series of constructions owned by the powerful Pamphili family, of Late Renaissance style. When the client, Giovanni Battista Pamphili became Pope in 1644 with the name of Innocenzo X, the family decided that the building was no longer enough for their new prestige, so they started a newer and bigger construction. Girolamo Rinaldi was commissioned the project. The new project embedded contiguous buildings, including the previous Pamphili Palace, whose decorations by Agostino Tassi were kept, at least partly, the Cybo Palace and the Mellini Palace.
The interior has three courtyards. The entrance is particularly high and bright: the ‘noble’ floor has 23 frescoed rooms by artists such as Giacinto Gemignani, Gaspard Dughet, Andrea Camassei, Giacinto Brandi, Francesco Allegrini, Pier Francesco Mola. In 1651 – 1654, Pietro da Cortona painted the long gallery, designed by Borromini, with the stories of Enea.