Prominent among the masters who were influenced by Donatello, the sculptor, and Lorenzo Ghiberti, the first metal-worker in elegant forms, is Paolo di Dono, generally known as Uccello. His profound study and ultimate discovery of the laws of linear perspective was enhanced by the inquiries into the laws of aerial perspective that Fra Angelico studied so deeply. Paolo Uccello (1397-1475) was a pupil and assistant of Lorenzo Ghiberti, who made the bronze doors for the East Side of the Baptistery at Florence. He gave himself up to the scientific study of perspective, the principles of which he was one of the first to apply to painting, thus rendering incalculable services to art. In his _Battlepiece_ (No. 1273) is seen a mounted soldier in armour with his sword drawn; on the left are horsemen about to charge with couchant lances, while on the right cavalry-men are drawn up awaiting orders, their lances in rest. The correctness of the perspective and the justice of the foreshortenings and the movements of the foot-men in the intervals of the cavalry mark an epoch in art. This is the third and right-hand panel of the series of three battle-pictures which Uccello painted for the Casa Medici (now the Riccardi Palace) in Florence for Cosimo de’ Medici about the year 1457, and not, as the official Catalogue asserts, for the Bartolini family. The best preserved of these three large panel pictures illustrating the _Rout of San Romano in 1432_ is that in the National Gallery (No. 583), while the second or centre panel of the series is now in the Uffizi (No. 52). The Louvre panel is in a deplorable condition, caused by long neglect. Uccello’s _Portraits of Giotto, Paolo Uccello, Antonio Manetti, and Filippo Brunelleschi_ (No. 1272), whose names are in this order on the panel, is a work of considerable importance, as marking an early stage in the development of portraiture. This picture, which is referred to at some length by Vasari, constitutes a historical document. The Italian chronicler tells us that Uccello “was a person of eccentric character and peculiar habits, but he was a great lover of ability in those of his own art, and, to the end that their memory should remain to posterity, he drew with his own hand on an oblong picture the portraits of five distinguished men, which he kept in his house as a memorial of them. The first of these portraits was that of the painter Giotto, as one who had given light and new life to the art; the second was Filippo di Ser Brunellesco, for architecture; the third was Donatello, for sculpture; the fourth was himself, for perspective and animals; the fifth was his friend Giovanni (_sic_) Manetti, for mathematics. With this philosopher Paolo conferred very frequently, and held continual discourse with him concerning the problems of Euclid.” Manetti’s real Christian name, Antonio, is correctly inscribed on the panel, but is inaccurately given as Giovanni by Vasari and on the official label.