In the 3rd or 4th century AD, a Martyrium was built over a tomb, supposedly that of John the Evangelist. A century later, a church with a wooden roof was built over the tomb. This church was damaged by an earthquake and in the 6th century, the Emperor Justinian (527-565 AD) constructed a six-domed church, which became an important place for pilgrimage. Because of the authorship of the Book of Revelation, John is intimately associated with the Church of Ephesus. He was, according to tradition, the first Bishop of Ephesus.
Here we see the massive substructure that supported the church in the west.