Edessa was an ancient city (polis) in Upper Mesopotamia, founded during the Hellenistic period by King Seleucus I Nicator, founder of the Seleucid Empire. It later became capital of the Kingdom of Osroene, and continued as capital of the Roman province of Osroene. During the Late Antiquity, it became a prominent center of Christian learning and seat of the Catechetical School of Edessa. During the Crusades, it was the capital of the County of Edessa.
