The old name for modern-day Sanliurfa/Urfa, a city in eastern Turkey.
Originally named Osroe (presumably after some local satrap, this being the Armenian form for Chosroes), Edessa proceeded through a number of names - it became in Syriac Ourhoï, in Armenian Ourhaï in Arabic Er Roha, commonly Orfa or Urfa, its present name.
Rebuilt under Seleucus Nicator, in 303 BCE, it was named Edessa, in memory of the ancient capital of Macedonia. For a brief period, under Antiochus IV, the town was called Antiochia by colonists from Antioch who had settled there.
Edessa later became the capital of the Abgar dynasty of the Kingdom of Osrhoene, from 132 BCE until 244.
In 197, Edessa was the site of a Christian council (Eusebius, Historia Ecclesiae, V:23)
Edessa moved back and forth between Arab and Byzantine hands, until 1099, when (during the First Crusade), it was taken by crusaders and made the capital of the Crusader County of Edessa. The crusaders held the city until 1144, when it was again captured, by the Turks. Since the twelfth century, the city has successively belonged to the Sultans of Aleppo, the Mongols, the Mamelukes, the Osmanlis, and the modern Turkish state.