One of Italy's finest Romanesque churches is filled with treasures. A rose window by the 13th-century sculptor Brioloto represents a wheel of fortune, with six of the spokes formed by statues depicting the rising and falling fortunes of mankind. The 12th-century porch is the work of Maestro Niccolò; it's flanked by marble reliefs by Niccolò and Maestro Guglielmo depicting scenes from the Old and New Testaments and from the legend of Theodoric. The bronze doors date from the 11th and 12th centuries; some were probably imported from Saxony and some are from Veronese workshops. They combine allegorical representations with scenes from the lives of saints. Inside, look for the 12th-century statue of San Zeno to the left of the main altar. In modern times it has been dubbed the "Laughing San Zeno" because of a misinterpretation of its conventional Romanesque grin. A justly famous Madonna and Saints triptych by Andrea Mantegna (1431–1506) hangs over the main altar, and a peaceful cloister (1120–38) lies to the left of the nave. The detached bell tower was begun in 1045, before the construction of much of the present church, and finished in 1173.