This basilica, which looks strangely like a small fortress, stands near one of medieval Rome's most important streets, the one used by the Popes to reach San Giovanni in Laterano. Probably dating back to the 6th century, it seems that it was dedicated to four saints martyred during Diocletian's persecutions.

Although the church was restructured many times, it was always held in great esteem by the popes, so much so that, in the 15^th century, Pope Martin V declared it a pontifical seat. In addition to the splendid cloister judged to be one of the most extraordinary in the whole of Rome, the church's importance today lies in the chapel of St. Silvester.
The rectangular chapel, with its vaulted ceiling, has a pavement decorated in the cosmatesque style and an important fresco cycle from the late 13^th century. The eleven paintings show the "Donation" of Constantine. This was the document by which Constantine supposedly legitimized the temporary power of the papacy but which was sensationally revealed to be a forgery in the 15th century.
Constantine is shown afflicted by a serious illness and treated with the blood of babies but to no avail, so he sets off to seek help from the Pope Silvester I. The Pope, cleansing him of his sins through baptism, miraculously saves the Emperor who thereby becomes converted to Christianity.
As a gesture of his gratitude, he donates the Western Empire to the church. These frescoes were a form of political propaganda and their purpose was to support the primacy of the pope over the Holy Roman Emperors.