The Basilica of St John was built in the 6th century by the emperor Justinian on Ayasuluk Hill, on the site believed to be the burial place of John the Evangelist, who is recorded as having spent his later years and died in Ephesus. At its height it was the seventh-largest church in Christendom — a cruciform basilica covered by six domes — and was for a thousand years a major pilgrimage destination.
The Seljuks turned it into a mosque in the 14th century, and an earthquake in 1402 finished the structure. Today the columns, the floor plan, and the marble apse are reconstructed enough to give a clear sense of the scale, and the views from the upper terraces — out over the Temple of Artemis, the Isa Bey Mosque, and the plain of Ephesus to the modern coast — are the best in Selçuk.