castellum

Castellum is a Latin term meaning a small fort or fortress. The word is a diminutive of castrum, and it is the source of the English word castle through later transmission of Latin military and architectural vocabulary. In Roman military usage, a castellum referred to a fortlet or fortified outpost, typically garrisoned and integrated into a broader frontier network. Castella ranged from simple earthworks to stone-walled compounds, and could include gates, ditches, ramparts, and a central area that might house headquarters or offices of the commanding officer. Many forts included separate water facilities, known as castellum aquae, built to supply the garrison. The plural forms are castella or castellums.

In archaeological practice, castellum denotes a specific type of Roman fortification site or a component of a fort, rather than a single standardized plan. On the Roman frontiers, castellums were established along roads and natural corridors to monitor movement, project power, and support troop movements; they are known from various provinces, including Britain, the Danubian frontier, North Africa, and the Levant.

Etymology and cognates: from Latin castellum, the diminutive of castrum, with cognates in Romance languages such as castillo or castello. The term is primarily used in scholarly contexts today to describe Roman military architecture and site stratigraphy.