tar . ▁It ▁had ▁been ▁held ▁by ▁the ▁Mo ors ▁since ▁ 1 3 3 3 . ▁The ▁sie ge ▁followed ▁years ▁of ▁inter mitt ent ▁conflict ▁between ▁the ▁Christian ▁kingdom s ▁of ▁Spain ▁and ▁the ▁Mo or ish ▁Em ir ate ▁of ▁Gran ada , ▁which ▁was ▁supported ▁by ▁the ▁Mar in id ▁s ultan ate ▁of ▁Mor oc co . ▁A ▁series ▁of ▁Mo or ish ▁defe ats ▁and ▁revers es ▁had ▁left ▁Gib ral tar ▁as ▁a ▁Mo or ish - h eld ▁enc lave ▁within ▁Cast ilian ▁territory . ▁Its ▁ge ographical ▁isol ation ▁was ▁compens ated ▁for ▁by ▁the ▁strength ▁of ▁its ▁fort ifications , ▁which ▁had ▁been ▁greatly ▁improved ▁since ▁ 1 3 3 3 . ▁Alfonso ▁brought ▁an ▁army ▁of ▁around ▁ 2 0 , 0 0 0 ▁men , ▁along ▁with ▁his ▁mist ress ▁and ▁their ▁five ▁il leg it imate ▁children , ▁to ▁dig ▁in ▁to ▁the ▁north ▁of ▁Gib ral tar ▁for ▁a ▁length y ▁sie ge . ▁In ▁the ▁New ▁Year ▁of ▁ 1 3 5 0 , ▁however , ▁b ub onic ▁pl ague ▁– ▁the ▁Black ▁Death ▁– ▁broke ▁out ▁in ▁the ▁Cast ilian ▁camp . ▁Alfonso ▁refused ▁to ▁abandon ▁the ▁sie ge ▁but ▁fell ▁victim ▁to ▁the ▁pl ague ▁on ▁ 2 7 ▁March ▁ 1 3 5 0 , ▁becoming ▁the ▁only ▁monarch ▁to ▁die ▁of ▁the ▁disease . ▁ ▁P rel ude ▁to ▁the ▁sie ge ▁Alfonso ▁XI ▁had ▁attempted ▁to ▁re take ▁Gib ral tar ▁in