Earliest of the four is the minor southern portal near the Campanile, over which the pigeons cluster and coo. Our Lady of the Pigeons, in the tympanum, is an excellent work of the school of Nino Pisano (Andrea's son), rather later than the middle of the Trecento. The northern minor portal is similar in style, with sculpture subordinated to polychromatic decoration, but with beautiful twisted columns, of which the two outermost rest upon grand mediæval lions, who are helped to bear them by delicious little winged _putti_. Third in order of construction comes the chief southern portal, the Porta dei Canonici, belonging to the last decade of the fourteenth century. The pilasters are richly decorated with sculptured foliage and figures of animals in the intervals between the leaves. In the tympanum above, the Madonna and Child with two adoring Angels--statues of great grace and beauty--are by Lorenzo di Giovanni d'Ambrogio, 1402. Above are Angels bearing a tondo of the Pietà. The Porta della Mandorla is one of the most perfect examples of Florentine decorative sculpture that exists. M. Reymond calls it "le produit le plus pur du génie florentin dans toute l'indépendance de sa pensée." It was commenced by Giovanni di Ambrogio, the chief master of the canons' gate; and finished by Niccolò da Arezzo, in the early years of the fifteenth century. The decorations of its pilasters, with nude figures amidst the conventional foliage between the angels with their wings and scrolls, are already almost in the spirit of the Renaissance. The mosaic over the door, representing the Annunciation, was executed by Domenico Ghirlandaio in 1490. "Amongst modern masters of mosaic," says Vasari, "nothing has yet been seen better than this. Domenico was wont to say that painting is mere design, and that the true painting for eternity is mosaic." The two small statues of Prophets are the earliest works of Donatello, 1405-1406. Above is the famous relief which crowns the whole, and from which the door takes its name--the glorified Madonna of the Mandorla. Formerly ascribed to Jacopo della Quercia, it is now recognised as the work of Nanni di Banco, whose father Antonio collaborated with Niccolò da Arezzo on the door. It represents the Madonna borne up in the Mandorla surrounded by Angels, three of whom above are hymning her triumph. With a singularly sweet yet majestic maternal gesture, she consigns her girdle to the kneeling Thomas on the left; on the right among the rocks, a bear is either shaking or climbing a tree. This work, executed slightly before 1420, is the best example of the noble manner of the fourteenth century united to the technical mastery of the fifteenth. Though matured late, it is the most perfect fruit of the school of Orcagna. Nanni died before it was quite completed. The precise symbolism of the bear is not easy to determine; it occurs also in Andrea Pisano's relief of Adam and Eve labouring, on the Campanile. According to St.