“The King to the sheriff, greetings. I command you that, without delay, you give possession to X of [description of land], concerning which there was a suit between him and Y in my court; because such land is adjudged to him in my court by battle.”
-Standard instruction from a 13^th-century  English court to the county sheriff, reporting the outcome of a trial by combat.

“The first combat was performed at the time and place accordingly with observation of all due ceremonies as so short a time would suffer, wherein both parties showed great courage by a desperate fight: In which Conor was slain and Teig hurt but not mortally, the more was the pity: Upon this Wednesday following Mortogh Cogge [O'Connor] appeared in the same place brought by the captains to the listes, and there stayed 2 hours making proclamation against his enemy by drum and trumpet, but he appeared not ... The only thing we commend in this action was the diligent travail of Sir Lucas Dillon and the Master of the Rolls, who equally and openly seemed to countenance the champions, but secretly with very good concurrence, both with us and between themselves, with such regard of her Majesty's service, as giveth us cause to commend them to your Lordships.”
-State papers Ireland 63/104/69, reporting what is believed to be the last trial by combat under the authority of an English monarch.

“Can it be possible that this ‘wager of battle’ is being seriously insisted on? Am I to understand that this monstrous proposition as being propounded by the bar—that we, the judges of the Court of King's Bench—the recognized conservators of the public peace, are to become not merely the spectators, but the abettors of a mortal combat? Is that what you require of us?”
-Chief Judge William Downes of the King’s Bench, in the case of O’Reilly v. Clancy (1815).

Few artifacts of legal history are derided as much as the “wager of battle,” the English legal term for what is more commonly known as “trial by combat.”  But for several centuries, judicially-sanctioned dueling was one of the few tools at the court’s disposal to adjudicate disputed issues of fact where other methods (such as record-keeping) failed or (as with modern forensic science) were unavailable.  It was used prominently in land disputes, which, in the pre-GPS era, were endemic.[1]

In “Trial By Battle,”[2] Peter Leeson, Professor of Economics and Law at George Mason University, provides a legal and economic analysis of the wager of battle, and even a spirited defense:

To modern observers trial by battle is an icon of medieval backwardness. Montesquieu called it ‘‘monstrous’’. The institution’s barbarity seems equaled only by its senselessness. As Richard Posner put it, ‘‘trial by battle’’ is one of those ‘‘legal practices that no one defends any more’’.
Almost no one. This paper defends trial by battle. It examines trial by battle in England as judges used it to decide property disputes from the Norman Conquest to 1179. I argue that judicial combat was sensible and effective. In a feudal world where high transaction costs confounded the Coase theorem, trial by battle allocated disputed property rights efficiently.[3]

The entire paper can be found here.  Also worth reading is Leeson’s defense of a related practice, the trial by ordeal, found in “Ordeals.”[4]

The last recorded trial by combat in English law took place in the 16^th century. However, despite numerous proposals in Parliament to abolish the wager of battle during the 17^th and 18^th centuries, the practice remained on the books.  It was successfully invoked by a defendant in an appeal of murder (a type of criminal prosecution for homicide conducted by a private party rather than the Crown) in 1818, in the case of Ashford v. Thornton.[5]  When the prosecuting party failed to participate in the duel, the defendant was acquitted and set free. The following year, Parliament banned the wager of battle.[6]

However, the Thirteen Colonies adopted the entirety of English common law upon independence in 1776 (except where that law was subsequently modified by state or federal statute).  Accordingly, it is an open question whether or not trial by combat is a valid form of dispute resolution under American law in states where it has not been expressly abolished by statute.[7]

For further information, see Eric Jager, The Last Duel: A True Story of Crime, Scandal, and Trial by Combat in Medieval France (Random House, 2004); George Nielson, Trial by Combat (W. Hodge, 1890).