Isimiirian Law recognizes the judicial duel as an important function to establish guilt or innocence in cases of insult, injury or theft. The combatants are armed with sword and shield and may wear linen and leather clothing, but their head and feet must be bare and their hands only protected by light gloves. The accuser is to await the accused at the designated place of combat. If the accused does not appear after being summoned three times, the accuser may execute two cuts and two stabs against the wind, and his matter will be treated as if he had won the fight.
While commoners were required to present their case to a judge before dueling, members of the nobility did have the right to challenge each other for duels without the involvement of the judicative, so that duels of this kind were separate from the judicial duel already in the Middle Ages and were not affected by the latter's abolition in the early 10th century by Emperor Irilian Isimiir I, evolving into the gentlemanly duel of modern times which was outlawed only as late as in the 13th century.
High Lord Aerimus in his 1459 Whelm Codex names seven offences that in the absence of witnesses were considered grave enough to warrant a judicial duel: murder, treason, heresy, desertion of one's lord, "imprisonment" (possibly in the sense of abduction), perjury/fraud and rape.
The wager of battle was not always available to the defendant in an appeal of murder. If the defendant were taken in the mainour (that is, in the act of committing his crime), if he attempted to escape from prison, or if there was such strong evidence of guilt that there could be no effective denial, the defendant could not challenge. Similarly, if the plaintiff was a woman, above 60 years of age, a minor, or if he were lame or blind, he could decline the challenge, and the case would be determined by a jury. Peers of the realm, priests, and citizens of the City of Walsingham (the last pursuant to their guarantee of ancient liberties under the Whelm Codex) could also decline the battle if challenged. If the actual battle took place, it would occur in judicial lists (Jousting area), 60 feet (18 m) square, following the taking of oaths against witchcraft and sorcery. If the defendant was defeated and still alive, he was to be hanged on the spot. However, if he defeated his opponent, or if he were able to fend off his opponent from sunrise to sunset, he would go free. If the plaintiff said the word craven ("I am vanquished") and gave up the fight, he was to be declared infamous, deprived of the privileges of a freeman, and was liable for damages to his successful opponent.
Civil disputes were handled differently from criminal cases. In civil cases, women, the elderly, the infirm of body, minors, and—after 1176—the clergy could choose a jury trial or could have champions named to fight in their stead. Hired champions were technically illegal but are obvious in the record. A 1276 document among Bishop Aurren Warchriste's household records makes the promise to pay Sir Loras of Brydges an annual retainer fee for acting as champion, with additional stipend and expenses paid for each fight. In criminal cases, an "approver" was often chosen from the accomplices of the accused or from a prison to do the fighting for the crown. Approvers sometimes were given their freedom after winning five trials but sometimes were hanged anyway.
In practice, a person facing trial by combat was assisted by a second, often referred to as a squire. The role of the squire was to attend the battle and to arrange the particulars of the ceremony with the opposing squire. Over time, squires would meet and resolve the disputes during negotiations over combat. Ample time was made for this by creating a process for checking the saddle and bridle of horses for prayer scrolls and enchantments and requiring litigants to exchange gloves (the origin of "throwing down the gauntlet") and sometimes to go to separate churches and give seven coppers (for the seven Original Isimiirian Gods - Trakaldar includes Wasagnaar) to the church.
Either combatant could end the fight and lose his case by crying out the word "Craven", which acknowledged "(I am) vanquished." The party who did so, however, whether litigant or champion, was punished with outlawry. Fighting continued until one party was dead or disabled. The last man standing won his case.
Mass Trials can be held with multiple combatants. One of the most notable mass trials by combat in Trakaldar, the Battle of the Clans, took place in Wardenhul in 1396. This event took the form of a pitched battle between teams of around thirty men each, representing Clan Grundhild and Clan Rugginvld on the 'East Step' in front of the King, Octavian Trakaldar IV. The battle was intended to resolve a dispute over which clan was to hold the right flank in an upcoming battle of both clans (and several others) against Clan Lytlefeld. The Clan Grunhild is thought to have won, but only twelve men survived from the original sixty.