Revelation 1:9b I, John…was on the island of Patmos for the word of God and for the testimony of Jesus Christ.
Patmos is a small island in the Aegean Sea, located 37 miles southwest of Miletus. The island was a political prison, a place of exile that Roman emperors used to put away dissidents. John was apparently such a one for the testimony he preached regarding the unique and supreme nature of Jesus Christ.