A gorge in field fortification is the "unexposed side of a fieldwork", typically the rear of an independent fieldwork or detached outwork in front of the main fortress or defensive position.

Straith describes three commonly used classes of field work: "works open at the gorge, works enclosed all round and lines." He lists the following as works open at the gorge:

Closed works are the redoubt, star fort and bastioned fort.

Gorges of 'half-closed works' were usually closed either by a parapet or stockade.