The imposing quadriportico, 70 meters long and composed of 150 columns, planned by Poletti, was concluded by Calderini. A colossal statue of Saint Paul stands right at the centre of the atrium and was sculpted by Giuseppe Obici (1807-1878).
The façade is decorated by mosaics which were done between 1854 and 1874 (based on the designs of Agricola and Consoni). They depict: in the lower section, Isaiah, Jeremiah, Ezekiel and Daniel and in the central section, the mystical Lamb surrounded by four rivers which symbolize the four Gospels, and by twelve lambs representing the twelve Apostles. In the upper section, Christ is situated between Peter and Paul.
There are three main doors. At the centre , is the monumental door in green bronze made by Antonio Maraini, which was placed here in 1931; to its right is the new Holy Door , made of golden bronze, created by the sculptor Enrico Manfrini and erected for the Jubilee of the year 2000.
1) The central door (7.48 meters x 3.35 meters) shows episodes relating to the lives and preachings of Sts Peter and Paul. A big cross with inlaid silver and embellished with stones of lapis lazuli overlays the door from side to side.
2) The Holy Door (3.71 meters x 1.82 meters) illustrates the theme of the Trinity. A Latin inscription at the bottom of the door reads: Ad sacram Pauli cunctis venientibus aedem – sit pacis donum perpetuoquoe salus. It is a beautiful couplet wishing: the gift of peace and eternal salvation to be granted to all those visiting Paul’s Holy Temple.