Demi-Lune / Ravelin

An outwork with a redan trace (two faces joining to form a salient angle) positioned opposite the curtain of the enceinte and separated from it by the main ditch. The rear of most demi-lunes was broken into two demi-gorges formed by the counterscarp of the main ditch. Faces of the demi-lune were usually directed on the shoulder angles of the enceinte bastions collateral to the curtain masked by the demi-lune in such a way that fire from the bastion faces defended the demi-lune ditch. The object of most demi-lunes was to oppose an attack against a bastion with strong outworks that placed the attacked bastion in a retired and flanked position. To attack a bastion protected by demi-lunes the besieging army would necessarily be compelled to extend their trenches to attack and capture two demi-lunes before being able to establish breaching batteries against the bastion.

	Trace of a Demi-Lune According to Vauban's First Method
AB, FE	Faces of the Bastions
BC, ED	Flanks of the Bastions
B, E	Shoulders of the Bastions
CD	Curtain
HG, KG	Counterscarp of the Main Ditch
NG	Capital of the Demi-Lune
NO, NP	Faces of the Demi-Lune
OG, PG	Demi-Gorges of the Demi-Lune
L, M	Points on Bastion Faces 6 yards
	from Shoulders on which Demi-Lune
	Faces are directed

January, 2003