Who was the Roman Emperor who first legalized Christianity and founded the first St Peter's in Rome?

· The construction of the old Basilica of St Peter's was begun by Constantine the Great between 319 and 333.

· Christianity was not actually legalised. It was not given a legal status until 380 in the Edict of Thesalonica by co-emperors Gratian, Theodosius I and Valenitinian II.

· Constantine was not the first emperor to decree the toleration of Christianity. The first emperor to do this was Galerius in the Edict of Toleration by Galerius of 311. In this he granted toleration, which meant that the Christians were given freedom to worship and the right to live safely (i.e., not to be persecuted).

· Co-emperors Constantine the Great and Licinius issued the Edict of Milan in 313. This reiterated the toleration of Christianity and extended it to all religions.

· The old Basilica of St Peter's no longer exists. It decayed due to neglect. The stones of its ruins were used to build the new Basilica of St Peter's in the late 16th and early 17th centuries.