Zengi recaptured Edessa in 1144, an event that helped spark the Second Crusade. Imad al-Din Zengi was the atabeg, or military governor, of Mosul and Aleppo and one of the most powerful Muslim rulers confronting the Crusader states.
Edessa was the first Crusader state, founded in 1098 during the First Crusade. It was also the northernmost, weakest, and most exposed of those states. In late 1144, its ruler, Joscelin II, had taken much of his army away to support an ally, leaving the city vulnerable. Zengi arrived on 28 November and began a siege supported by siege engines and mining operations.
The city fell on 24 December 1144 after part of its walls collapsed. The conquest shocked Western Europe because Edessa was the first major Crusader state to fall. Pope Eugene III later issued the bull Quantum praedecessores in 1145, calling for the Second Crusade, led by Louis VII of France and Conrad III of Germany.
A common mix-up is confusing Zengi with his son Nur ad-Din or with Saladin. Those rulers became prominent later; Zengi was the leader responsible for Edessa’s 1144 capture.