portraits of two Italian princes, Sigismondo Pandolfo Malatesta and Federigo of Urbino, masterpieces[167] of fidelity to nature and sound workmanship. In addition to the many great paintings that command our admiration, Piero claims honour as the teacher of Melozzo da Forli and of Luca Signorelli. Little is left to show the greatness of Melozzo; but the frescoes preserved in the Quirinal are enough to prove that he continued the grave and lofty manner of his master.[168] Signorelli bears a name illustrious in the first rank of Italian painters; and to speak of him will be soon my duty. It was the special merit of these artists to elevate the ideal of form and to seek after sublimity, without departing from the path of conscientious labour, in an age preoccupied on the one hand with technicality and naturalism, on the other with decorative prettiness and pietism. While the Florentine and Umbro-Tuscan masters were perfecting the arts of accurate design, a similar direction toward scientific studies was given to the painters of Northern Italy at Padua. Michael Savonarola, writing his panegyric of Padua about 1440, expressly mentions Perspective as a branch of philosophy taught in the high school;[169] and the influence of Francesco Squarcione, though exaggerated by Vasari, was not inconsiderable. This man, who began life as a tailor or embroiderer, was early interested in the fine arts. Like Ciriac of Ancona, he had a taste for travel and collection,[170] visiting the sacred soil of Greece and sojourning in divers towns of Italy, everywhere making drawings, copying pictures, taking casts from statues, and amassing memoranda on the relics of antiquity as well as on the methods practised by contemporary painters. Equipped with these aids to study, Squarcione returned to Padua, his native place, where he opened a kind of school for painters. It is clear that he was himself less an artist than an amateur of painting, with a turn for teaching, and a conviction, based upon the humanistic instincts of his age, that the right way of learning was by imitation of the antique. During the course of his career he is said to have taught no less than 137 pupils, training his apprentices by the exhibition of casts and drawings, and giving them instruction in the science of perspective.[171] From his studio issued the mighty Andrea Mantegna, whose life-work, one of the most weighty moments in the history of modern art, will be noticed at length in the next chapter. For the present it is enough to observe that through Squarcione the scientific and humanistic movement of the fifteenth century was communicated to the art of Northern Italy. There, as at Florence, painting was separated from ecclesiastical tradition, and a new starting-point was sought in the study of mathematical principles, and the striving after form for its own sake.