Often copied, this is the Jesuit church par excellence. It combines the solemnity and simplicity of the Counter-Reformation with some incredibly exuberant interior decoration from a century later, at the very height of Baroque movement. Baciccia's frescoes painted on the nave vault and the chapel of St Ignatius by Andrea Pozzo are wonderful. Some like it and some don't (Stendhal hated it), but it should be seen!