It's Anglio-Saxon law that pre-dates the conquest
The King's Peace initially applied to the special protections accorded to the King's household and retainers. It expanded in the 10th and 11th centuries to particular times (such as holidays), places (such as highways and churches), and individuals (such as legates).
Following the Norman Conquest, the "king's peace" had extended to refer to "the normal and general safeguard of public order" in the realm, although specially granted peaces continued to be given after this period. Under the Leges Edwardi Confessoris (Laws of Edward the Confessor), the four great highways of the realm (the Roman roads of Watling Street, Icknield Street, Ermine Street, and Fosse Way) as well as navigable rivers were also under the king's peace. The Leges Edwardi Confessoris provided that the weeks for Christmas, Easter, and Pentecost were under the king's peace as well. Maitland commented that the king's peace had begun to "swallow up lesser peaces" such as the peaces of local lords of the manor. For example, roads other than the four great Roman roads were formerly under the sheriffs' peace, but by the end of the 14th century had been brought under the king's peace.
The binding over power of magistrates, which was first codified in the Justices of the Peace Act 1361, has partial roots in the early use of sureties of the peace, which "emerged from the peace-keeping arrangements of Anglo-Saxon law, extended by the use of the royal prerogative and royal writs to bestow the king's peace where the king wished until the peace became a nationwide legal reality." Sureties of the peace were replaced in the 13th and 14th centuries, as the institutions of keeper of the peace and then justice of the peace were established. The 19th-century legal commentator James Fitzjames Stephen wrote that the conservators of the king's peace were the king, the great officers of state, and the King's Bench on the national level, and the sheriffs, coroners, justices of the peace, and constables on the local level.