What is a crenellation?
What are embrasures?
What are merlons?
On a castle or fort, a battlement or a crenellation is a parapet with open spaces for shooting. The raised portions of a battlement are called merlons, and the openings are called embrasures. Masonry buildings in the Gothic Revival style may have architectural decoration which resembles battlements.
Castle with battlement (crenellation)
Illustration from ArtToday.com
