Sentence:  The "Half-Moon" is a Work always raiſed before the Baſtion's Point, being ſo named from the Lowneſs of its Gorges Cavity, &c. and is to ſecure the Two Faces of the Baſtion; but when the Faces have but a weak Defence from the "Ravelin", theſe Works are ſoon made uſeleſs or ruined, and give the Beſieged an opportunity of Lodgment, and may ſerve for Batteries and Flanks againſt the oppoſing Baſtions; however they may be retrenched by Traverſes, yet they will not fail to attack entirely in the Face, or where you have your laſt <WSD>Retrenchment</WSD>, alſo that called the Counterguard runs the like Hazard. 
Meaning of the word marked with <WSD> tags:  A defensive work constructed within a fortification to make it more defensible (by allowing defenders to retreat into and fight from it even after the enemy has taken the outer work).