- A bombproof chamber, usually of masonry, in which cannon may be placed, to be fired through embrasures; or one capable of being used as a magazine, or for quartering troops.
- A hollow molding, chiefly in cornices.
A casemate is a fortified gun emplacement or armored structure from which guns are fired, originally a vaulted chamber in a fortress. The word comes from the Italian casamatta, meaning "armed house", with the origins being in the words for "casa" (house) and "matta" (dull, dark or dim). In civilian use a casemate may be a tunnel cut into a rock face with armoured doors, used for storing volatile goods. In civilian architecture the term is also used to describe a hollow molding, used mostly in a cornice.
In naval gunnery a casemate is a vertical armour plate with openings for guns. It is less protected than a gun turret and allows for a smaller field of fire. It is however much cheaper in terms of money and far lighter in weight for a given level of armor protection.
The American Civil War saw the use of casemate ironclads: steel-built or armored steamboats with a very low freeboard and their guns on the main deck ('Casemate deck') protected by a sloped armored casemate. Although both sides of the civil war used casemate ironclads, the ship is mostly associated with the southern confederacy, the north more relying on turretted monitors. The most famous naval battle of the war being the duel at Hampton Roads between the Union turretted ironclad USS Monitor and the Confederate casemate ironclad CSS Virginia (built from the scuttled remains of the Merrimack)
In 20th century battleships, casemates were used to mount secondary guns for defending the ship against torpedo boats. In practice, these guns were generally quite useless; usually mounted close to the water, casemate guns were often awash in spray, and sometimes swamped completely by the ship's rolling. More modern designs did away with casemate weapons entirely, favoring extra topside turret mounts for their secondary batteries.
casemate in Czech: Kasematy
casemate in German: Kasematte
casemate in Croatian: Kazamat
casemate in Italian: Casamatta
casemate in Dutch: Kazemat
casemate in Norwegian: Kasematt
casemate in Polish: Kazamata
casemate in Russian: Каземат
casemate in Finnish: Kasematti
casemate in Swedish: Kasematt