Edessa (; Ancient Greek: Ἔδεσσα, romanized: Édessa) was an ancient city (polis) in Upper Mesopotamia, in what is now Urfa or Şanlıurfa, Turkey. It was founded during the Hellenistic period by Macedonian general and self proclaimed king Seleucus I Nicator (r. 305–281 BC), founder of the Seleucid Empire. He named it after an ancient Macedonian capital. The Greek name Ἔδεσσα (Édessa) means "tower in the water". It later became capital of the Kingdom of Osroene, and continued as capital of the Roman province of Osroene. In 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.
The city was situated on the banks of the Daysan River (Ancient Greek: Σκίρτος; Latin: Scirtus; Turkish: Kara Koyun), a tributary of the Khabur, and was defended by Şanlıurfa Castle, the high central citadel.
Ancient Edessa is the predecessor of modern Urfa (Turkish: Şanlıurfa; Kurdish: Riha; Arabic: الرُّهَا, romanized: ar-Ruhā; Armenian: Ուռհա, romanized: Urha), in Şanlıurfa Province, Turkey. Modern names of the city are likely derived from Urhay or Orhay (Classical Syriac: ܐܘܪܗܝ, romanized: ʾŪrhāy / ʾŌrhāy), the site's Syriac name before the re-foundation of the settlement by Seleucus I Nicator. After the defeat of the Seleucids in the Seleucid–Parthian Wars, Edessa became capital of the Kingdom of Osroene, with a mixed Syriac and Hellenistic culture. The origin of the name of Osroene itself is probably related to Orhay.
The Roman Republic began exercising political influence over the Kingdom of Osroene and its capital Edessa from 69 BC. It became a Roman colonia in 212 or 213, though there continued to be local kings of Osroene until 243 or 248. In Late Antiquity, Edessa was an important city on the Roman–Persian frontier with the Sasanian Empire. It resisted the attack of Shapur I (r. 240–270) in his third invasion of Roman territory. The 260 Battle of Edessa saw Shapur defeat the Roman emperor Valerian (r. 253–260) and capture him alive, an unprecedented disaster for the Roman state. The Late Antique Laterculus Veronensis names Edessa as the capital of the Roman province of Osroene. The Roman soldier and Latin historian Ammianus Marcellinus described the city's formidable fortifications and how in 359 it successfully resisted the attack of Shapur II (r. 309–379).
The city was a centre of Greek and Syriac theological and philosophical thought, hosting the famed School of Edessa. Edessa remained in Roman hands until its capture by the Persians during the Byzantine–Sasanian War of 602–628, an event recorded by the Greek Chronicon Paschale as occurring in 609. Roman control was restored by the 627 and 628 victories of Heraclius (r. 610–641) in the Byzantine–Sasanian War, but the city was lost by the Romans again in 638, to the Rashidun Caliphate during the Muslim conquest of the Levant. It did not return to the Romans' control until the Byzantine Empire temporarily recovered the city in the mid-10th century after a number of failed attempts.
The Byzantine Empire regained control in 1031, though it did not remain under their rule long and changed hands several times before the end of the century. The County of Edessa, one of the Crusader states set up after the success of the First Crusade, was centred on the city, the crusaders having seized the city from the Seljuks. The county survived until the 1144 Siege of Edessa, in which Imad al-Din Zengi, founder of the Zengid dynasty, captured the city and, according to Matthew of Edessa, killed many of the Edessenes. The Turkic Zengid dynasty's lands were eventually absorbed by the Ottoman Empire in 1517 after the 1514 Battle of Chaldiran.
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