Coastal defence and fortification

Coastal defence (or defense) and coastal fortification are measures taken to provide protection against military attack at or near a coastline (or other shoreline), for example, fortifications and coastal artillery. Because an invading enemy normally requires a port or harbour to sustain operations, such defences are usually concentrated around such facilities, or places where such facilities could be constructed.

Source: Wikipedia — Coastal defence and fortification (CC BY-SA 4.0)