The term 'military structure' can be summarized as a fortified defensive structure, such as a FORT. A FORT is a defensive structure built to protect a military base or settlement from attack. Forts are typically made of stone, brick, or concrete and are usually surrounded by a wall or other barrier. They are often equipped with artillery and other weapons to defend against enemy forces. Forts have been used throughout history to protect cities, towns, and other settlements from attack.