In Europe, at least, it would appear to be a Germanic custom. It was in use among the ancient Geats, Goths, Svear, and Franks, but it was generally unknown in Roman law and does not figure in the Torah or the laws of Hammurabi. Extensive statutes governing its use appear in the capitularies of Louis the Pious, king of the Franks, in 819.
As it existed in the mediŠval laws of western Europe, it was typically explained as a judicium Dei, the judgment of God. In theory, the trial so conducted would yield a just result because God would strengthen the arm of the combatant who was in the right. In this, it resembled trial by ordeal, which were a number of hazardous tests whose outcome would indicate guilt or innocence; these outcomes, too, were God's verdicts. It seems likelier that since in the days of feudalism, weak central governments and no standing armies, conflicts between nobles could lead to minor wars, a judicially organised duel was a less expensive substitute that gave the litigants the public and physical satisfaction they wished.
Wager of battel, as the trial by combat was called in English, appears to have become part of the common law of England in the Norman conquest. The earliest case in which wager of battel is recorded is Wulfstan v. Walter (1077), eleven years after the Conquest. Significantly, the names of the parties suggest that it was a dispute between a Saxon and a Norman. Ranulf de Glanvill's De Legibus et Consuetudinibus AngliŠ, from around 1187, appears to have considered it the chief mode of trial, at least among aristocrats entitled to bear arms.
When Henry II reformed English civil procedure in the Assize of Clarendon in 1166, trial by jury became available, and lawyers, guarding the safety of the lives and limbs of their clients, steered people away from the wager of battel. A number of legal fictions were devised to enable litigants to avail themselves of the jury even in the sort of actions that were traditionally tried by wager of battel.
Wager of battel remained in two forms of action dear to the honour bound hearts of the aristocracy, however. The first was the writ of right, the most direct way at common law of challenging someone's right to a piece of real property. The second was the criminal appeal, which was not, like the contemporary appeal, a proceeding in a court of superior jurisdiction reviewing the proceedings of a lower court. Rather, the criminal appeal was a private criminal prosecution instituted by the accuser directly against the accused.
Such a private prosecution was last conducted in the case of Ashford v. Thornton (1818). Pronouncing judgment in favour of the accused's plea claiming the wager of battel, Justice Bayley of the King's Bench said that:
One of the last actual trials by combat, the Battle of the Clans, took place in Perth in 1396. This event took the form of a pitched battle between teams of around thirty men each, representing Clan Chattan and Clan Kay on the North Inch in front of the King, Robert III. Clan Chattan is thought to have won but only twelve men survived from the original sixty.
Trials by combat at common law in England were carried on with quarterstaffs, on a duelling ground of sixty feet square. Each litigant was allowed a rectangular, leathern shield, and could be armed with a suit of armour, provided that they were bare to the knees and elbows, and wore only red sandals on their feet. The litigants appeared in person; women, the elderly, the infirm of body, and minors could have champions named to fight in their stead. The combat was to begin before noon, and be concluded before sunset. Before fighting, each litigant had to swear an oath disclaiming the use of witchcraft for advantage in the combat, which oath is in words and figures as follows: