A 'toothed' upper edge to a parapet wall. see Crenel & Merlon
Another term for battlements, but used to describe decorative battlements. Often these are made of ashlar or fine brick and include arrow slits. Many later medieval houses and churches were crenellated, like Oxbrugh Hall and Jesus College, Cambridge.
Found on http://www.architecture.com/HowWeBuiltBritain/Glossary.xhtml
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