"Paolo Uccello employed himself perpetually and without any
intermission," says Vasari, "in the consideration of the most difficult
questions connected with art, insomuch that he brought the method of
preparing the plans and elevations of buildings, by the study of linear
perspective, to perfection. From the ground plan to the cornice, and
summit of the roof, he reduced all to strict rules, by the convergence
of intersecting lines, which he diminished towards the centre, after
having fixed the point of view higher or lower, as seemed good to him;
he labored, in short, so earnestly in these difficult matters that he
found means, and fixed rules, for making his figures really to seem
standing on the plane whereon they were placed; not only showing how in
order manifestly to draw back or retire, they must gradually be
diminished, but also giving the precise manner and degree required for
this, which had previously been done by chance, or effected at the
discretion of the artist, as he best could. He also discovered the
method of turning the arches and cross-vaulting of ceilings, taught how
floors are to be foreshortened by the convergence of the beams; showed
how the artist must proceed to represent the columns bending round the
sharp corners of a building, so that when drawn in perspective, they
efface the angle and cause it to seem level. To pore over all these
matters, Paolo would remain alone, almost like a hermit, shut up in his
house for weeks and months without suffering himself to be approached."