The modern French word for crenel is créneau, also used to describe a gap of any kind, for example a parking space at the side of the road between two cars, interval between groups of marching troops or a timeslot in a broadcast.
Such licences were granted by the king, and by the rulers of the counties palatine within their jurisdictions, e.g. by the Bishops of Durham and the Earls of Chester and after 1351 by the Dukes of Lancaster.
A list of licences issued by the English Crown between the 12th and the 16th centuries was compiled by Turner & Parker and expanded and corrected by Philip Davis and published in The Castle Studies Group Journal.
[6][4] They could, however, provide a basic deterrent against wandering bands of thieves, and it is suggested that the function of battlements was comparable to the modern practice of householders fitting highly visible CC TV and burglar alarms, often merely dummies.
[4] Battlements may be stepped out to overhang the wall below, and may have openings at their bases between the supporting corbels, through which stones or burning objects could be dropped onto attackers or besiegers; these are known as machicolations.
In the European battlements of the Middle Ages the crenel comprised one-third of the width of the merlon: the latter, in addition, could be provided with arrow-loops of various shapes (from simply round to cruciform), depending on the weapon being utilized.
Italian military architects used the so-called Ghibelline or swallowtail battlement, with V-shaped notches in the tops of the merlon, giving a horn-like effect.
Many South Asian battlements are made up of parapets with peculiarly shaped merlons and complicated systems of loopholes, which differ substantially from rest of the world.
The battlements of the Arabs had a more decorative and varied character, and were continued from the 13th century onwards not so much for defensive purposes as for a crowning feature to the walls.
A further decorative treatment appears in the elaborate paneling of the merlons and that portion of the parapet walls rising above the cornice, by the introduction of quatrefoils and other conventional forms filled with foliage and shield.