I of the Principality of Antioch. This contravention of the agreement to return conquered lands to the emperor's control, was justified in the crusaders' letter to Pope Urban II by the statement that the Greek Christians were heretics. Later, Bohemond took the opportunity of a crusade to attack Dyrrachium (Durrës), justifying his attack on the Christians in a letter to Pope Paschal II enumerating Alexios's faults and blaming him for the EastWest Schism and for having taken the imperial throne by force. Besides Guibert, other crusader writers to accuse Eastern Christians of sabotaging the crusade include Raymond of Aguilers, Albert of Aix, Baldric of Dol, and the author of the Gesta Francorum. Alexios's departure from the crusade, followed by the departure of his envoy Tatikios, was seen as proof of the Eastern Christians' treachery. Though Fulcher of Chartres displayed a positive assessment of Eastern Christianity, he too accused the emperor of attacking Christian pilgrims, and of being a "tyrant". When First Crusade's Siege of Jerusalem ended successfully for the crusaders, the patriarchate of Jerusalem was vacant, and the crusaders elevated a Latin patriarch without reference to either the Roman Catholic or the Eastern Orthodox churches. An Orthodox candidate for the patriarchate was forced to flee to Constantinople. Only when Saladin's Siege of Jerusalem was concluded and the city was returned to Muslim control were the Orthodox Christians allowed to practise in the Church of the Holy Sepulchre. Crusade scholars continue to debate crusading, its causes, and its effects, so scholarship in this field repeatedly undergoes revision and reconsideration. Many early crusade scholars saw the source-histories as simple recitations of how events actually transpired, but by the eighteenth and nineteenth centuries, scholarship was increasingly skeptical of that assumption. By 1935, Carl Erdmann published Die Entstehung des Kreuzzugsgedankens (The Origin of the Idea of Crusade), changing the direction of crusader studies more than any other single work by focusing on the ideology of crusade. This ideology indicated the crusades were essentially defensive, which meant that soldiers were there to provide protection for pilgrims and fellow Christians in the East and to reclaim formerly Christian lands lost to Islamic expansion and forced conversion. This ideology remained throughout the Middle Ages despite the failure to finalize these goals. Constable adds that those "scholars who see the crusades as the beginning of European colonialism and expansionism would have surprised people at the time. Crusaders would