CHAPTER XXII. PIERO DELLA FRANCESCA. It is not by dwelling exclusively on the growth of the purely Florentine school that we shall explain its deve lopment. Its ultimate perfection was due to the wisdom with which all past and cotemporary elements of progress were assimilated and combined, from whatever quarter they might originally proceed. The great laws of com position founded on the models of Giotto, the plastic ele ment made dominant by the sculptors of the fifteenth century, the scientific perspective of lines, which owed its grand impulse to Uccelli, the more subtle one of atmo sphere which Masaccio mastered, the tasteful architecture revived by Brunelleschi and Alberti, were summed up in a great measure by the spirit and grasp of Domenico Ghirlandaio. The changes in the use and application of mediums carried out by the Peselli and Baldovinetti, enlarged and extended by the Pollaiuoli, gained a con crete value in Verrocchio. But the merit of these and later artists owed much to the example of one who is not a Florentine, though educated in his earliest years under the tuition of a master formed on the pure Flor entine models. Pietro di Benedetto of the Franceschi, more commonly known as Piero della Francesca, was bom at Borgo San Sepolcro in Umbria, on the Western face of the moun tain chain which parts Tuscany from the old duchy of Urbino and the States of the church on the Adriatic coast. He might have reached the twentieth year when he laboured at Florence, and the date of his birth may there-