In the Roman Republic and the Roman Empire, the Latin word castrum[1] (plural castra) referred to a building, or plot of land, used as a fortified military base. In English, the terms "Roman fort", "Roman camp" and "Roman fortress" are commonly used for castrum. However, scholastic convention tends toward the use of the words "fort", "camp", "marching camp" or "fortress" to translate castrum.[2]

Templeborough Roman Fort in South Yorkshire visualised 3D flythrough, produced for Rotherham Museums and Archives.

Romans used the term castrum for different sizes of camps - including large legionary fortresses, smaller forts for cohorts or for auxiliary forces, temporary encampments, and "marching" forts. The diminutive form castellum was used for fortlets,[3] typically occupied by a detachment of a cohort or a centuria.

For a list of known castra, see List of castra.