A procedure introduced into English law in the later 12th century by Henry II. The Assize of Clarendon (1166), which dealt with criminal trials, and the Assize of Arms (1181), which reorganized local defence and police measures, were enactments made at sessions of the king’s council. The assizes of novel disseisin and mort d’ancestor (both relating to tenancy), and the Grand Assize (to determine titles to disputed lands) were introduced by sessions of Henry II’s council (1166, 1176, and the late 1170s); these procedures remained important throughout the Middle Ages.

Travelling justices were established in the 13th century; these justices came to be called justices of assize and their sessions were called assizes. A system of such judicial sessions was regularized (1293–1328) and judicial circuits were established that remained in force until a new system of Crown Courts was set up in 1971.