Fortification, n.
Etymology: [L. fortificatio : cf. F. fortification.]
1. The act of fortifying; the art or science of fortifying places in order to defend them against an enemy.
2. That which fortifies; especially, a work or works erected to defend a place against attack; a fortified place; a fortress; a fort; a castle. Fortification agate, Scotch pebble.
Syn. -- Fortress; citadel; bulwark. See Fortress.
Shades of meaning
Fortification is the general word for any artificial defensive work; a fortress is a fortification of especial size and strength; a fortress is regarded as permanent, and is ordinarily an independent work; a fort or fortification may be temporary; a fortification may be but part of a defensive system; we speak of the fortifications of a city. A citadel is a fortification within a city, or the fortified inner part of a city or fortress, within which a garrison may be placed to overawe the citizens, or to which the defenders may retire if the outer works are captured; the medieval castle was the fortified residence of a king or baron. Fort is the common military term for a detached fortified building or enclosure of moderate size occupied or designed to be occupied by troops. The fortifications of a modern city usually consist of a chain of forts. Any defensible place, whether made so by nature or by art, is a fastness or stronghold.