The Basilica of Saint Paul Outside the Walls is the largest religious building located in the city of Rome after Saint Peter's Basilica in the Vatican. It seems that the original paleo-Christian building was built in the time of Constantine and the mortal remains of Saint Paul of Tarsus were kept there. The basilica was built on the land occupied by an ancient necropolis in which, according to documentary sources, the remains of Saint Paul rested. It seems that in this place a small cubicle was erected –cella memoriae- where the first Christians worshiped the disciple of Christ.
The place became a center of pilgrimage from the 1st century AD. and due to its heyday in the fourth century, around the year 306 or 307, Emperor Constantine decided to build a new sanctuary. The building erected by the emperor was located two kilometers from the wall of Rome -hence the name of Saint Paul Outside the Walls- it was the typical religious construction whose typology was faithfully represented in the basilica. With a rectangular floor plan divided into three naves whose only semicircular apse contained the tomb of Saint Paul. The architecture soon turned out to be, again, too small for the faithful who came to the temple and the following emperors chose to demolish the building and erect a new, more majestic construction. of the building ofConstantine barely preserved a small part that can be seen today in the apse of the current Basilica of San Pablo.
The works of the new building, known as the Theodosian building, were directed by Sallust the perfect of the city and executed by the master Cirade. The building followed the same scheme as the previous one, the basilica model materialized this time in a basilica with five naves and a single apse that over time became the temple of one of the most outstanding monastic complexes in Rome. Over time some modifications were made to the construction (the pavement was raised with respect to the original height, an access was placed from the direct transept to the saint's tomb…) but in its conception it remained unchanged so that in the 19th century it was one of the oldest Christian buildings in all of Europe.
In 1823, a fire caused by a worker who was restoring the roof of the basilica destroyed the building, destroying practically the entire building. The temple was left in such precarious conditions that virtually the entire wall had to be repaired; the works were entrusted to Giusepe Valadier and were carried out according to the restorative theories of the time so that today it is not easy to differentiate the original remains of Valadier's project. A new building with five naves and a single apse was erected that stylistically responds to the parameters of the neoclassical style. Among the remains of the primitive construction was found asarcophagus that supposedly should house the remains of the disciple although it has not yet been verified.