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The crusades were intended to seize Jerusalem from Muslim control. The First Crusade was proclaimed by Pope Urban II (pope 1088–99) at the Council of Clermont in 1095 in response to a request from the Byzantine Emperor Alexios I Komnenos (r. 1081–1118) for aid against further Muslim advances. Urban promised indulgence to anyone who took part. Tens of thousands of people from all levels of society mobilised across Europe and captured Jerusalem in 1099. One feature of the crusades was the pogroms against local Jews that often took place as the crusaders left their countries for the East. These were especially brutal during the First Crusade, when the Jewish communities in Cologne, Mainz, and Worms were destroyed, and other communities in cities between the rivers Seine and Rhine suffered destruction. Another outgrowth of the crusades was the foundation of a new type of monastic order, the military orders of the Templars and Hospitallers, which fused monastic life with military service.

What Byzantine Emperor's request for assistance led to the First Crusade?
Alexios I Komnenos