Pius directed Bernardo Rossellino to model the cathedral after a church that he had seen on his travels in Austria.
The façade combines elements of both medieval and classical architecture.
The reason for this is that the church's Austrian model was a hallenkirche (hall church), a popular type in Germany and Austria that is distinguished from the traditional basilican church by having side aisles that are as high as the nave.
The continuity in height between the nave and side aisle enabled Rossellino to design a simple pitched roof with a central gable. Because the framing members are detailed as cornices, the gable resembles a pediment, and in combination with the colossal pilasters that project from the wall plane, suggests the end of a Classical temple.
This similarity is contradicted by a number of other features.
Although much of the façade's vocabulary has classical roots, the manner in which the forms are combined is decidedly unclassical.
The two rows of small-scale columns in combination with arches form a decorative system that expresses neither the cathedral's vaulted structure nor the façade's suggestion of a temple.
Rossellino's variation from standard classical usage on this façade can be appreciated by comparing it with Alberti's church façades from that time such as the Malatesta Temple, Santa Maria Novella, and Sant' Andrea.
The proportionate height of the compound piers (piers resembling a cluster of columns) was based on the piers of the basilica's Austrian model.
The pedestal bases originally intended to serve as bases were accidentally omitted, and to make up for their height without reconstructing them, vertical members were positioned above the piers.
The pope concluded that this novelty contributed to the cathedral's individual character.
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