The Assize of Clarendon was an act of Henry II of England in 1166 that began a transformation of English law and led to trial by jury in common law countries worldwide, and that established assize courts.
Prior systems for deciding the winning party in a case, especially felonies, included trial by ordeal, trial by battle, or trial by compurgation (trial by oath), in which evidence, inspection, and inquiry was made under oath by laymen, knights or ordinary freemen. After the Assize of Clarendon trial by jury developed, though some historians say beginnings of the jury system predate this act. The Assize of Clarendon did not lead to this change immediately; recourse to trial by combat was not officially rescinded until 1819, though by then it had fallen out of use.
The assize takes its name from Clarendon Palace, Wiltshire, the royal hunting lodge at which it was promulgated.
In 1154, Henry II inherited the throne of a troubled England. In full swing were the Crusades, a military endeavour that kept noble landowners away from their castles for years at a time. Unoccupied and unclaimed land invited squatters; since there was no central recording office for real property in England at the time, and sorting out who owned what fief was entrusted to human memory, disputes arose when aristocrats returned or died thousands of miles from home.
Another, even more, serious was the aftermath of The Anarchy, a disastrous civil war between King Stephen and the Empress Matilda. The two factions had hired mercenary soldiers, and when there was no one left to pay them, many resorted to robbery and other forms of violence as a profession. Crime followed the breakdown of the local authority. The quarrel between the King and the Empress created more property troubles; as communities were divided, both factions were happy to reward their supporters with the lands of the local opponents.
Finally, there was the long-standing difficulty involving the Catholic Church, which culminated in the murder of Thomas Becket, the Archbishop of Canterbury.