The basilica was first built in the middle of the 5th century to house the relic of the chains that bound Saint Peter while imprisoned in Jerusalem.

According to legend, when Empress Eudoxia (wife of Emperor Valentinian III) gave Pope Leo I the chains as a gift, he compared them to the chains of St. Peter's first imprisonment in the Mamertine Prison in Rome and the two chains miraculously fused together.

The chains are kept in a reliquary under the main altar in the basilica.