Of ancient foundation, the church of Sant' Agnese in Agone was rebuilt by Girolamo Rainaldi and his son Carlo, at the behest of Pope Innocent X (r. 1644-55), whose family palace stood next door. In 1653 the pair were replaced by Francesco Borromini, who added the splendid concave facade. He, too, was soon replaced and the work was completed by Giovanni Maria Baratta, who added the twin bell towers. The facade sports a single statue, that of St Agnes.
The layout of the interior is based on a Greek cross plan.
The fresco in the cupola depicts The Apotheosis of St Agnes and is mostly the work of the Roman painter Ciro Ferri (1634-89), a pupil of Pietro da Cortona. However, Ferri died before finishing the fresco and this task fell to his pupil Sebastiano Corbellini. The pendentives were painted by Giovanni Battista Gaulli (1639-1709), better known as il Baciccio or il Baciccia, and depict allegories of the four Cardinal Virtues. The inscription at the base of the dome reads: INGRESSA AGNES TVRPITVDINIS LOCVM ANGELVM DOMINI PREAPARATVM INVENIT(On entering the place of shame, Agnes found the angel of the Lord ready).
The seven altarpieces all take the form of bas-reliefs or statues rather than paintings. The high altar sports a bas-relief of The Holy Family with St John the Baptist and his Parents (1683) by Domenico Guidi. The altar is surmounted by three putti holding a bronze scroll, which reads: NON SVRREXIT INTER NATOS MVLIERVM MAIOR IOANNE BAPTISTA(None has arisen among the sons of women greater than John the Baptist), a possible reference to the pope who was born Giovanni Battista Pamphilj.
The Chapel of St Agnes occupies the right arm of the Greek cross. The statue of St Agnes Among the Flames is by Ercole Ferrata (1610-86). The flames represent the fires of sexual temptation. Above the vault are a pair of angels carrying the symbols of martyrdom (palm branch and crown), also the work of Ferrata. Above these he executed three putti holding a text proclaiming: IN MEDIO IGNIS NON SVM AESTVATA (In the middle of the fire I am not burned).
The Chapel of St Sebastian occupies the left arm. The statue of St Sebastian (c. 1703) is by Pier Paolo Campi (1668-1764).
The four small chapels, which are sited in the piers supporting the dome, are dedicated to St Cecilia (top left), St Emerentiana (top right), St Alexis (bottom right) and St Eustace (bottom left).
A small chapel at the back of the church houses the putative skull of St Agnes.
High above the main entrance is the funerary monument (1730) to Pope Innocent X, the work of the sculptor Giovanni Battista Maini (1690-1752).