He began by erecting the piers which were intended to support the central dome; but working hastily and without due regard to solid strength, Bramante made these piers too weak to sustain the ponderous mass they had to carry.

How he would have rectified this error cannot be conjectured.

Death cut his labours short in 1514, and only a small portion of his work remains embedded at the present day within the mightier masses raised beneath Buonarroti's cupola.
Leo X.commissioned Raffaello da Urbino to continue his kinsman's work, and appointed Antonio da Sangallo to assist him in the month of January 1517.

Whether it was judged impossible to carry out Bramante's project of the central dome, or for some other reason unknown to us, Raffaello altered the plan so essentially as to design a basilica upon the conventional ground-plan of such churches.

He abandoned the Greek cross, and adopted the Latin form by adding an elongated nave.