"In March 1095, the devastation incurred by the onstorming Seljuk Turks in the Byzantine territories forced Emperor Alexius I to ask Pope Urban II for help. This request inspired Urban’s preaching of the crusades later that year at the church council of Clermont. Urban’s crusading plans were in great part a striving to restore good relations with the Byzantine church and was not one which had premeditated plans for expanding the Latin Church. So the expressed goal of Urban’s call was to help Alexius I regain Byzantine territories lost to Seljuk forces.
During the first Crusade the papal legate Adhémar of Le Puy was present among the Crusaders to enforce Alexius’ desire that those lands re-conquered would be given back to the Byzantines. An additional condition was that any other lands gained through their efforts would likewise become part of the Byzantine empire.
The seemingly carte blanche Urban offered Alexius through the Crusader’s unconditional help was a result of the papacy’s views of the Eastern church. At this time both Rome and Constantinople were still seen as a single church in communion with each other. The Crusader’s had no other stipulated goals than to restore the Byzantine sees to the holiest sites of Christianity.
The West’s intentions of goodwill were demonstrated when Crusaders conquered portions of North Syria in 1097. When Antioch was taken the patriarch Symeon II was restituted to the position. This appointing of a Byzantine to the see confirms Rome’s intentions. The joint statement issued by Adhémar and Symeon II further points to the cooperation of both churches. Rome and Constantinople were acting as one body."
Source: dissertation Sebastián Ernesto Salvadó, August 2011, Stanford University. Illustration: A mitred Adhémar de Monteil carrying the Holy Lance in one of the battles of the First Crusade; source Wikipedia.