The 145 × 30 m-big three-aisled bishop’s church of the city was erected in the southern stoa of the Olympieion Quarter. The Basilica is re-known for the 3rd Ecumenical Council (Mary as the God-bearer) in AD 431. The church has been rebuilt numerous times until the late Byzantine period.
The bishop’s seat was St. John’s Basilica latest in the 7th century, whereas the Church of Mary was used as a burial church well into the Medieval Period.