Renaissance gave currency, is a mistake. In inserting the entablature block at the arch impost Alberti did not follow a rule always observed in the ancient times. This feature is uncommon in ancient Roman art. It was, as before remarked, introduced by the late Roman architects, who, being accustomed to the use of the entablature over the column in the trabeate system which they had borrowed from the Greeks, did not see, when they began to spring arches from columns, that the entablature had no longer any reason for existence. The radical nature of the change wrought in architecture by the introduction of the arch was never grasped by the imperial Roman designers. First framing the arch with an order, thus uniting two contradictory systems, they afterwards, when, as in the basilica of Maxentius, springing the arches of vaulting from columns, thought that the rules required them to crown these columns with bits of entablature.
This façade appears to have been originally designed in the Pisan Romanesque style, with a tall, shallow blind arcade on pilaster-strips reaching across the ground story. But the Romanesque character was modified in some details, the portals having pointed arches, pointed arched niches sheltering tombs being ranged in the intervals between the pilaster-strips. How far the upper part of this façade had been left incomplete until Alberti took it in hand we have no means of knowing; but no mediæval features occur in it as it "now stands, except the circular opening in the central compartment. Upon this front, then, Alberti appears to have ingrafted the great Corinthian order, placing a wide pilaster paired with a column on each angle, breaking the entablature into ressauts to cover the columns, which have nothing else to support, and replacing the central portal with the existing one in the revived classic style. The preservation of the greater part of the mediæval work in the ground story made it impossible to get in more than the four columns in the great order, and these are necessarily spaced in an unclassic way, with a narrow interval in the middle and very wide ones on either side. To the upper compartment the architect has given an order of pilasters surmounted by a classic pediment, and flanked by screen walls over the aisle compartments in the form of gigantic reversed consoles, apparently the first of these features which became common thereafter in
