Platea in the Byzantine Period
This island, which the Byzantines called "Plati" (flat) or "Platea" because of its flat appearance, was used as a surveillance base, and was also one of the most feared exile places throughout the Byzantine history.
There aren’t many historical records about Yassıada between the 4th to the 9th centuries. Yassıada Monastery was built by the Byzantine emperor Theophilos (829-842) by 840
Later, the famous cleric Ignatius, who served as the Patriarch of Istanbul between 867 and 877, had a church built for the Kirk Saints and an altar for the Virgin Mary in 860. There are four large cellars under the church that were used as a prison after the 10th century.