After the edict of Milan of 313, which granted Christians freedom of worship, Emperor Constantine decided to donate two basilicas to the new nascent Church, erected on the tombs of Saints Peter and Paul.
However, in the 5th century, the three reigning emperors of the time, Theodosius, Valentinian II and Arcadius, seeing that the constant flow of pilgrims was too much for the original basilica to cope with, had to construct a larger building. In doing so the orientation of the basilica was changed so that it faced west.
It was only in 1854 that Pope Pius IX inaugurated the present monumental basilica which contains the chain, which, according to tradition, bound the Apostle Paul to the Roman Soldier who was guarding him while he was imprisoned awaiting trial.