merlo

Merlon comes from the Italian merlo (a battlement, a blackbird), possibly from the Latin merulus (blackbird). The connection between a blackbird and a stone block is obscure — one theory suggests that the profile of a merlon resembles a perched bird. Another derives it from the Latin moenia (walls) through a diminutive form. The word entered English through Italian military engineering texts in the sixteenth century.

A merlon is the raised section of a battlement. The gaps between merlons are embrasures or crenels. Together, they form the crenelated profile that defines castle architecture in every children's drawing. The merlon protects the defender. The crenel allows the defender to shoot. The alternating pattern — solid, gap, solid, gap — is the most recognizable feature of a fortified building.

Merlon design varied by region and period. English merlons were typically rectangular. Italian merlons were often swallowtail-shaped — bifurcated at the top. In the Papal States, Guelph merlons were rectangular (supporting the Pope) and Ghibelline merlons were swallowtail-shaped (supporting the Emperor). The shape of a block of stone on a wall encoded political allegiance during the wars between Guelphs and Ghibellines.

Crenelation rights were legally restricted in medieval Europe. In England, a crenelation license (licentia crenellandi) was required from the crown to add battlements to a building. The right to put merlons on your wall was a royal prerogative. Without permission, a merlon was an act of rebellion.