||This article includes a list of references, but its sources remain unclear because it has insufficient inline citations. (September 2011)|
A merlon forms the vertical solid parts of a battlement or crenellated parapet—in Medieval architecture of fortifications for millennia. Merlons are sometimes narrowly pierced by vertical embrasure "slits" to view and fire through. When a wider space is between two merlons it is called a crenel, and a series of many merlon—crenels creates crenellation. Crenels designed in later eras, for use by cannons, were called embrasures.
The word comes from the French language, adapted from the Italian merlone, possibly a shortened form of mergola, connected with Latin mergae (pitchfork), or from a diminutive moerulus, from murus or moerus (a wall). An alternative etymology suggests that the medieval Latin merulus (mentioned from the end of the 10th century) functioned as a diminutive of Latin merle, expressing an image of blackbirds sitting on a wall.
As part of battlements 
As an essential part of battlements, merlons were used in fortifications for millennia. The best-known examples appear on mediaeval buildings, where battlements, though defensive, could be attractively formed, thus having a secondary decorative purpose. Some (especially later) buildings have false "decorative battlements". The two most notable European variants in Middle Ages merlons shape were the Ghibelline and the Guelph merlon: the former ended in the upper part with a swallow-tailed form, while the latter term indicates the normal rectangular shape merlons (wimperg).
Other shapes include: three-pointed, quatrefoil, shielded, flower-like, rounded (typical of Islamic and African world), pyramidal, etc., depending either from the type of attacks expected or aesthetic considerations.
In Roman times, the merlons had a width sufficient to shelter a single man. As new weapons appeared in the Middle Ages (including crossbows and the first firearms), the merlons were enlarged and provided with loop-holes of various dimensions and shapes, varying from simply rounded to cruciform. From the 13th century, the merlons could also be used to pivot wooden shutters; these added further protection for the defenders when they were not firing, or were firing downwards near the base of the wall. The shutters (also known as "mantlets") could be opened by hand, or by using a pulley.
Usage of merlons, from Eugène Viollet-le-Duc's Dictionnaire raisonné de l’architecture française du XIe au XVIe siècle.
Guelphs merlons in the Castle of Montechino, Italy.
Guelph merlons in the Mackenzie castle, Genoa.
Later use 
After falling out of favour when the invention of the cannon forced fortifications to take a much lower profile, they re-emerged as decorative features in buildings constructed in the neo-Gothic style of the 19th century.
See also 
- J. E. Kaufmann; H. W. Kaufmann; Robert M. Jurga (2004). The medieval fortress: castles, forts and walled cities of the Middle Ages. Da Capo Press. p. 307. ISBN 978-0-306-81358-0.
- Ward Bucher (1996). Dictionary of building preservation. Wiley-Interscience. pp. 43, 126, and 165. ISBN 978-0-471-14413-7.
- Balestracci, D. (1989). "I materiali da costruzione nel castello medievale". Archeologia Medievale (XVI): pp. 227–242.
- Luisi, R. (1996). Scudi di pietra, I castelli e l’arte della guerra tra Medioevo e Rinascimento. Bari. ISBN 88-420-5083-0.
|Wikimedia Commons has media related to: Merlons|