A wall around a city, built to define the city's boundaries, and sometimes to protect it from aggressors.
A fortified place; a large and permanent fortification, sometimes including a town; for example a fort, a castle; a stronghold; a place of defense or security.
A position that, if obtained by the weaker side, will prevent penetration by the opposing side, generally achieving a draw.
To furnish with a fortress or with fortresses; to guard, to fortify.