The Basilica of San Giovanni Maggiore is a church in Largo San Giovanni Maggiore in central Naples, Italy. A 4th-century church at the site was likely erected sometime in the 4th century. There are a number of founding legends for the church. One is that emperor Constantine I founded the church in gratitude for the rescue of his daughter Costanza from a shipwreck. It may have been built or introduced into a pre-existing pagan temple dedicated to the cult of Hercules or Hadrian. One of the stones in the architrave is dated to 324. The church underwent numerous reconstructions, including in the 6th century. It was likely made into a Byzantine-style basilica during the era of Belisarius.