Named after San Donato and San Pietro, the Cathedral is a masterpiece of Tuscan Gothic architecture. The building was begun in 1278 by the Bishop of Arezzo, Guglielmo degli Ubertini, thanks to a financial bequest left by Pope Gregory X who died in the city on 10 January 1276. The façade was only started at the beginning of the 20th century and remains incomplete. The very characteristic bell tower was constructed between 1857 and 1937. The lofty, slender space of the interior is harmoniously divided into an elegant nave and two aisles, and they mystically culminate in the apse which is embellished by great cuspated windows and the beautiful, finely finished marble altar. The fresco of Mary Magdalen, painted by Piero della Francesca, is not to be missed. Close by is the funeral monument to Bishop Tarlati made in 1330 by Agostino di Giovanni and Angelo di Ventura. The stained glass windows by Guillaume de Marcillat are marvellously composed and coloured, as are the Della Robbia terracotta works in the neoclassical Chapel of Our Lady of Comfort. The Cathedral possesses numerous other works by such renowned artists as Giorgio Vasari and Donatello. Atop the majestic lines of steps leading up to the Cathedral stands a statue of the Grand Duke Ferdinand I de Medici, modelled in 1594 by the renowned sculptor, born Jean de Boulogne but known everywhere as Giambologna (1529-1608).