With his letter to the Persian Mari, Ibas of Edessa († 457) got caught up between the millstones of the different dogmatic positions in the 5th century Christological conflict. This monograph on the Bishop of Edessa creates a vivid picture of a neglected chapter in church history and the history of dogma. In a unique manner, it combines regional aspects with the history of ideas in the Eastern Mediterranean. The resultant picture of Ibas invites a reassessment of traditional prejudices in the ecumenical discussion.