Popes might issue briefs to the effect that his plans should be followed; but when it was discovered that, during his lifetime, he kept the builders in ignorance of his intentions, and that he left no working models fit for use, except in the case of the cupola, a free course was opened for every kind of innovation.

So it came to pass that subsequent architects changed the essential features of his design by adding what might be called a nave, or, in other words, by substituting the Latin for the Greek cross in the ground-plan.

He intended to front the mass of the edifice with a majestic colonnade, giving externally to one limb of the Greek cross a rectangular salience corresponding to its three semicircular apses.

From this decastyle colonnade projected a tetrastyle portico, which introduced the people ascending from a flight of steps to a gigantic portal.

The portal opened on the church, and all the glory of the dome was visible when they approached the sanctuary.