What is Assize Of Arms Of 1252?

Legal Definition
The Assize of Arms of 1252, also called the Ordinance of 1252, was a proclamation of King Henry III of England concerning the enforcement of the Assize of Arms of 1181, and the appointment of constables to summon men to arms, quell breaches of the peace, and to deliver offenders to the sheriff.

Along with the Ordinance of 1233 that required the appointment of watchmen, the appointment of constables has been cited as one of the earliest creation of the English police, as has the Statute of Westminster 1285.
-- Wikipedia