Proof, a cornerstone of any legal system, archaic or modern, has always been a vexing problem in the long development of the rule of law. In medieval times, as we shall see, types of proof, such as eyewitness evidence, and means of establishing facts to prove something, such as inquests and hearings, were part of courtroom procedure; today's tribunals consider similar material. Early medieval legal life, however — not far removed from the practices of Franconian tribal law, where the ordeal was known, and not yet influenced by the great revival of Roman law in the twelfth century — relied, as well, on what we would call irrational proofs such as the oath, as it was understood at that time, and ordeal.

The heyday of the ordeal in medieval European society lasted from 800 to around 1200. Beginning with the Carolingians, who were strong proponents of its employment, the use of the ordeal increased markedly, in part because of government's advocacy of its use; new varieties of the ordeal, such as the ordeal of the cross; and expansion into new areas. While the ordeal, which had its European roots in Frankish society, had attracted criticism from the ninth century onward, it had performed a useful judicial function for certain types of cases until clerical participation in it was forbidden by the Fourth Lateran Council in 1215, shortly after the probable date of composition of Gottfried's Tristan.