What does "fortress" mean?

Fortress: A fortified place; a large and permanent fortification, sometimes including a town; a fort; a castle; a stronghold; a place of defense or security. A fortress is constructed for military purposes only, and is permanently garrisoned; a fortification is built to defend harbors, cities, etc.; a castle is a fortress of early times which was ordinarily a palatial dwelling; a citadel is the stronghold of a fortress or city, etc.

Additional senses

  1. 2.To furnish with a fortress or with fortresses; to guard; to fortify. Shak.

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