Selçuk Kalesi was built on the hill Ayasoluk on which a settlement probably already existed in Hittite times. Whether it was identical with Apasa, the temporary capital of Arzawa, mentioned in Hittite sources, is controversial. Excavations on Ayasoluk Hill showed that there was continuous settlement from the early Bronze Age to the Hellenistic period. This proves that ancient Ephesus was on Ayasuluk Hill.

In the seventh century A.D., the port of Ephesus was once again abandoned and the city threatened by Arab incursions. The Byzantines moved the town back to the area around the hill, where the Church of St. John was built in the sixth century.

The date of construction of the fortress cannot be exactly reconstructed, but the nature of the masonry can be used to deduce that it was built in the sixth century, i.e. in the Byzantine period. The building, like the town, was later taken over by the Seljuks, who converted the castle into a Byzantine-Seljuq mixing plant.

The citadel is surrounded by a ring wall closed at the top with a crenellated ring. The wall is reinforced by 15 towers and has one gate in the south and one in the north. Inside there are several cisterns, a Byzantine church ruin and a mosque from the Seljuk period. The largest diameter of the complex is about 160 m in north-south direction.