Complex sentence: In 313 the Edict of Milan established religious freedom in the empire, ending persecution of the Christians, and in 403 the Saint-Sernin basilica opened as a shrine for relics of Saint Saturnin.
Split into simpler sentences: In 313 the Edict of Milan established religious freedom in the empire, ending persecution of Christianity. In 403 the Saint-Sernin basilica was opened to serve as a shrine for the relics of Saint Saturnin.