During the later twelfth and thirteenth centuries, justices mainly from the central courts at Westminster, were sent to hold courts for all types of pleas in the counties of England. The counties were grouped into circuits, each of which was ridden by a small group of justices under commission to the king.
Primary among these were the justices in eyre, but the eyres were held too infrequently to enable routine criminal or civil business to be dealth with on a regular basis in the counties. The chief difficulty was that trial by assize or jury required the presence of twelve or more men from the vicinity where the matter in question occurred. As a result, in the twelfth and thirteenth centuries a wide range of more limited commissions developed for hearing the pleas of the crown. Commissions of oyer and terminer were established to inquire into, hear and determine the facts of the specified offenses, while commissions of gaol delivery tried or released prisoners in specified gaols. On the civil side, justices were commissioned to officiate at petty assizes which were set up to deal with disputes between parties and required a body of men summoned from the vicinity to answer questions put to them relative to the case.