Coastal artillery is the branch of armed forces

Armed forces

The armed forces of a country are its government-sponsored defense, fighting forces, and organizations. They exist to further the foreign and domestic policies of their governing body, and to defend that body and the nation it represents from external aggressors. In some countries paramilitary...

 concerned with operating anti-ship artillery

Artillery

Originally applied to any group of infantry primarily armed with projectile weapons, artillery has over time become limited in meaning to refer only to those engines of war that operate by projection of munitions far beyond the range of effect of personal weapons...

 or fixed gun batteries

Artillery battery

In military organizations, an artillery battery is a unit of guns, mortars, rockets or missiles so grouped in order to facilitate better battlefield communication and command and control, as well as to provide dispersion for its constituent gunnery crews and their systems...

 in coastal fortifications.

It has been held as a general rule of thumb, that one shore-based gun equalled three naval guns of the same caliber, due to the steadiness of the coastal gun which allowed for significantly higher accuracy than their sea-mounted counterparts. Land-based guns also benefited in most cases from the protection of walls or earth mounds which gave the guns an added measure of protection.
One of the first registered uses of coastal artillery was in 1381 - during the war between Ferdinand I of Portugal

Ferdinand I of Portugal

Ferdinand I , sometimes referred to as the Handsome or rarely as the Inconstant , was the ninth King of Portugal and the Algarve, the second son of Peter I and his wife, Constance of Castile...

 and Henry II of Castile - when the troops of the King of Portugal used cannon

Cannon

A cannon is any piece of artillery that uses gunpowder or other usually explosive-based propellents to launch a projectile. Cannon vary in caliber, range, mobility, rate of fire, angle of fire, and firepower; different forms of cannon combine and balance these attributes in varying degrees,...

s to defend Lisbon

Lisbon

Lisbon is the capital city and largest city of Portugal with a population of 545,245 within its administrative limits on a land area of . The urban area of Lisbon extends beyond the administrative city limits with a population of 3 million on an area of , making it the 9th most populous urban...

 against an attack from the Castilian naval fleet.

The use of coastal artillery expanded during the Age of Discoveries, in the 16th century; when a colonial power took over an overseas territory, one of their first tasks was to build a coastal fortress, both to deter rival naval powers and to subjugate the natives.