This famed 17th-century piazza, built over the site and following the form of the 1st-century Stadium of Domitian, is one of Rome's showpiece attractions. It still has the carefree air of the days when it was the scene of Roman circus games, medieval jousts, and 17th-century carnivals. Today it often attracts fashion photographers and Romans out for their evening passeggiata (promenade). The Christmas fair held from early December through January 6 fills the piazza with games, nativity scenes (some well crafted, many not so), and multiple versions of the Befana, the ugly but good witch who brings candy and toys to Italian children on Epiphany. (Her name is a corruption of the Italian word Epifania.) Bernini's splashing Fontana dei Quattro Fiumi (Fountain of the Four Rivers), with an enormous rock squared off by statues representing the four corners of the world, makes a fitting centerpiece. Behind the fountain is the church of Sant'Agnese in Agone, an outstanding example of baroque architecture built by the Pamphili Pope Innocent X and still owned by his descendants, the Doria Pamphili. The facade -- a wonderfully rich mélange of bell towers, concave spaces, and dovetailed stone and marble -- is by Carlo Rainaldi (1611-91) and Francesco Borromini (1599-1667), a contemporary and sometime rival of Bernini. One story has it that the Bernini statue nearest the church, which represents the River Plate, has its hand up before its eye because it can't bear the sight of the Borromini facade. Though often repeated, the story is a fiction: the facade was built after the fountain.