Gundumar Edessa ita ce ta farko a cikin jahohin ‘yan Salibiyya da aka kafa a lokacin da kuma bayan yakin Crusade na farko .Ya kasance daga 1098 lokacin da Baldwin na Boulogne ya bar babban sojojin Crusade na farko kuma ya kafa nasa sarauta.Edessa shi ne ya fi kowa arewa, mafi rauni, kuma mafi karancin jama’a;don haka, ana kai hare-hare akai-akai daga kasashen musulmi da ke kewaye da Ortoqids, Danishmends, da Seljuk Turkawa suka yi mulki.An kama Count Baldwin II da Joscelin na Courtenay na gaba bayan sun sha kaye a yakin Harran a shekara ta 1104. An kama Joscelin a karo na biyu a shekara ta 1122, kuma ko da yake Edessa ya murmure kadan bayan yakin Azaz a shekara ta 1125, an kashe Joscelin a yakin. a shekara ta 1131. An tilasta wa magajinsa Joscelin II shiga kawance da Daular Rumawa , amma a shekara ta 1143 duka Sarkin Byzantine John II Comnenus da Sarkin Urushalima Fulk na Anjou sun mutu.Joscelin ya kuma yi jayayya da Raymond II na Tripoli da Raymond na Poitiers, wanda ya bar Edessa ba shi da wani kawaye mai karfi.Zengi, wanda ya riga ya nemi ya yi amfani da mutuwar Fulk a shekara ta 1143, ya yi gaggawar zuwa arewa don kewaye Edessa, ya isa ranar 28 ga Nuwamba. An gargadi birnin game da zuwansa kuma an shirya don kewaye, amma babu kadan da za su iya yi yayin da Joscelin da sojojin sun kasance a wani wuri.Zengi ya kewaye birnin gaba daya, ya gane cewa babu wani soja da ke kare shi.Ya gina injuna na kewaye ya fara tona katangar, yayin da dakarun Kurdawa da na Turcoman suka hada da sojojinsa.Mazaunan Edessa sun yi tsayin daka gwargwadon iyawarsu, amma ba su da gogewa a yaƙin kewaye;Hasumiyai masu yawa na birnin sun kasance babu mutum.Har ila yau, ba su da masaniya game da hakar ma'adinai, kuma wani bangare na katangar da ke kusa da kofar Sa'o'i ya ruguje a ranar 24 ga watan Disamba. Sojojin Zengi sun shiga cikin birnin, inda suka kashe duk wadanda suka kasa guduwa zuwa Kasuwar Maniaces.Labarin faduwar Edessa ya isa Turai, kuma tuni Raymond na Poitiers ya aika da tawaga ciki har da Hugh, Bishop na Jabala, don neman taimako daga Paparoma Eugene III.A ranar 1 ga Disamba, 1145, Eugene ya ba da sanarwar fasfo Quantum praedecessores yana kira ga Crusade na biyu .