The huge Gesù is the flagship church of the Jesuits, the order founded by Basque soldier Ignatius Loyola in the 1530s. Realising the power of a direct appeal to the emotions, Loyola devised a series of 'spiritual exercises' aimed at training devotees to experience the agony and ecstasy of the saints. The Gesù itself (built 1568-84) was designed to involve the congregation as closely as possible in the proceedings, with a nave unobstructed by aisles, offering a clear view of the main altar. Giacomo della Porta added a façade that would be repeated ad nauseam on Jesuit churches across Italy (and the world) for decades afterwards.
As befitted a construction of the immediate post-Reformation era - with Martin Luther's fulminations against material manifestations of God's glory still echoing - the Gesù started out life as a very austere affair. Over the next century, however, there was much embellishment. A large, bright fresco, Triumph in the Name of Jesus, by Il Baciccia (1676-79) - one of Rome's great Baroque masterpieces - decorates the gilded ceiling of the nave, which seems to dissolve on either side as stucco figures (by Antonio Raggi) and other painted images are sucked up into the dazzling light of the heavens. (The figures falling back to earth are presumably Protestants.)
On the left is another spectacular Baroque achievement: the chapel of Sant'Ignazio (1696-1700) by Andrea Pozzo, which is adorned with gold, silver and coloured marble; the statue of St Ignatius is by Antonio Canova. Towering above the altar is what was long believed to be the biggest lump of lapis lazuli in the world… in fact, it's covered concrete. Check out the sculpture group to the left and prepare to wince: an ugly hag (Idolatry) has her breast tugged by a vicious serpent as a virtuous Faith triumphs over them and a pagan Roman soldier. Outside the church, at piazza del Gesù 45, you can visit the rooms of St Ignatius, which contain a wonderful painted corridor with trompe l'oeil special effects by Pozzo, and mementoes of the saint, including his death mask.