A defensive structure enclosing a city, castle, etc. Chiefly plural, fortifications.

The wall surrounding (or formerly surrounding) a town. Also in plural in same sense.

A wall or fence. The wall of a city, a fortification. Obsolete.

A fortification, a wall.

Fortification. Now historical. The part of a defensive wall between two bastions; the outward-looking side of a curtain (cf. curtain, n.1 4a).

Fortification. The plain wall of a fortified place; the part of the wall which connects two bastions, towers, gates, or similar structures. complement…

An outer fortification, esp. one belonging to a city or castle; a barbican. Also occasionally in extended use.