St. Severin is a Lutheran parish church in Keitum on the island of Sylt, northern Germany. It was named after the 4th-century bishop Severin of Cologne. Built in the Romanesque style and first documented in 1240, the church stands back from the town at a higher elevation. Tests have shown that the roof of the church can be dated to 1216, making it the oldest religious building in Schleswig-Holstein. The tower was built around 1450 and served as a navigation mark for seafarers as well as a prison.