The quintessence of Baroque architecture, this church has a facade that is a wonderfully rich mélange of bell towers, concave spaces, and dovetailed stone and marble. It's the creation of Francesco Borromini (1599–1667), a contemporary and rival of Bernini. Next to his new Pamphilj family palace, Pope Innocent X had the adjacent chapel expanded into this full-fledged church. The work was first assigned to the architect Rainaldi. However, Donna Olimpia, the pope's famously domineering sister, became increasingly impatient with how the work was going and brought in Borromini, whose wonderful concave entrance has the magical effect of making the dome appear much larger than it actually is. The name of this church comes from the Greek agones, the source of the word navona and a reference to the agonistic competitions held here in Roman times. The saint associated with the church is Agnes, who was martyred here in the piazza's forerunner, the Stadium of Domitian. As she was stripped nude before the crowd, her hair miraculously grew to maintain her modesty before she was killed. The interior is a marvel of modular Baroque space and is ornamented by giant marble reliefs sculpted by Raggi and Ferrata.