Covering blushes

Burnished Rows of Steel, Chapter 3 Part 2:

the covered face, a half-built but existing earthwork that defended the shore approaches to Montgomery... Unfortunately for the British, however, Parrott had emplaced several rifled guns in embrasures cut into the covered face

Textbook of Fortification and Military Engineering, for use at the Royal Military Academy, Woolwich, Part I (1877):

Counterguards are works intended to protect the faces of bastions... When they are so narrow as to be suitable only for musketry they are termed couvrefaces; such narrowness has the advantage that the besieger has no room to establish breaching batteries upon them.

Of course, you can tell through observation that the covered face is too narrow to mount artillery. However, in light of TFSmith's pretensions to academic status, it's nice to know that a covered face is by its very definition too narrow to mount artillery.