The Fourth Crusade was a unique event that stood out among all other Crusades. It was conceived as a victorious return of the warriors of Christ on a mission to recapture Jerusalem from the Muslim infidels, thus providing a much-needed lifeline to the overseas Christian kingdoms. But the Fourth Crusade actually ended with the fall of Constantinople, the capital of the largest Christian empire of the time, and the birth of the Latin Empire from the millennium-old ruins of Orthodox Byzantium.

The consequences of the Fourth Crusade for the peoples of the Orthodox world have not been thorougly studied and there is a significant gap in the use of important written sources and archaeological data regarding the Fourth Crusade. This thesis makes use of Orthodox-Slavonic texts published only recently to explore the attitude of Orthodox nations towards the Crusade and the changes that had occurred in spiritual and everyday life after the fall of Constantinople. The thesis also analyses Latin written sources that inform our understanding of the diplomatic and religious infighting between the Latin Empire, Bulgaria, and the three Greek statelets that succeeded the Byzantine Empire. It includes the first English translation of some texts and traces the crusade’s impact on the daily life of the Orthodox nations using evidence obtained through little-known and unpublished archaeological data from dozens of settlements and fortresses in what is now southern Bulgaria, then part of the erstwhile Latin Empire. Combining archaeological evidence with all available written sources chronicling the campaign enables the fullest possible reconstruction of the Fourth Crusade. This approach recovers unknown facts, events, and battles involving the knights of the Fourth Crusade and corroborates the veracity of all the written sources about the Fourth Crusade by identifying and including archaeological artefacts discovered at locations described by mediæval chroniclers.