In fortifications a demi-lune is a type of ravelin work constructed beyond the main ditch of a fortress, and in front of the curtain between two bastions, intended to defend the curtain. Research Demi-lune
In fortifications outworks are minor defences constructed beyond the main body of a work. Examples include ravelin, lunette, hornwork, etc. Research Outwork
In fortifications a ravelin is a detached work with two embankments which make a salient angle. It is raised before the curtain on the counter-scarp of the place. Research Ravelin
 
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