Northwest of the Lower Gate, a signposted path leads to the ruins of the Church of St Mary, also called the Double Church. The original building was a Hall of the Muses, a place for lectures, teaching and debates. Destroyed by fire, it was rebuilt as a church in the 4th century – the first one named after the Virgin Mary.
Later it served as the site of the Council of Ephesus (AD 431), which condemned the Nestorian heresy which refused to refer to Mary as the 'Mother of God'. Over the centuries several other churches were built here, somewhat obscuring the original layout. The rubble at the exit from the church area is a pile of milestones that once indicated distances to and from Ephesus.