Odo of Deuil (1110 – April 18, 1162) was a French monk who participated in the Second Crusade (1147–1149), and served as the chaplain of Louis VII on the expedition. His narrative of the Crusade is titled De profectione Ludovici VII in Orientem (On Louis VII's Journey to the East), which relates the progress of the crusade from France to Antioch.
Odo blamed the Byzantine Empire under Manuel Comnenus for the downfall of the crusade. Odo's prejudice against Byzantium led Steven Runciman to describe Odo as "hysterically anti-Greek" (A History of the Crusades). However, J. Phillips has recently argued that Odo's view of Byzantium was possibly rooted in ideological differences which minor skirmishes between the crusaders and Greeks had brought to the fore ("Odo of Deuil's De profectione Ludovici VII in Orientem as a source for the Second Crusade", The Experience of Crusading). His prejudice should also be set against the experience of Conrad III of Germany, who wrote that Manuel treated him as a "brother" when he served as his physician in Constantinople when he came down with an illness in Ephesus.
Below is an excerpt from De profectione Ludovici VII in Orientem, (translated by V. Berry New York, Columbia University Press, 1948, p. 57):
If our priests celebrated mass on Greek altars, the Greeks afterwards purified them with propitiatory offerings and ablutions, as if they had been defiled. All the wealthy people have their own chapels, so adorned with paintings, marble, and lamps that each magnate might justly say, "O Lord, I have cherished the beauty of Thy house." ... But, O dreadful thing! We heard of an ill usage of theirs which could be expiated by death; namely, that every time they celebrate the marriage of one of our men, if he has been baptized in the Roman way, they rebaptize him before they make the pact. We know other heresies of theirs, both concerning their treatment of the Eucharist and concerning the procession of the Holy Spirit. ... Actually, it was for these reasons that the Greeks had incurred the hatred of our men, for their error had become known even among the lay people. Because of this they were judged not to be Christians, and the Franks considered killing them a matter of no importance and hence could with the more difficulty be restrained from pillage and plundering.
It was such prejudice and ideological difference that led to the sacking of Constantinople in the Fourth Crusade of 1204.