| This article is part of the series on: Military of ancient Rome (portal) 753 BC – AD 476 |
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| Structural history | |
|---|---|
| Roman army (unit types and ranks, legions, auxiliaries, generals) | |
| Roman navy (fleets, admirals) | |
| Campaign history | |
| Lists of wars and battles | |
| Decorations and punishments | |
| Technological history | |
| Military engineering (castra, siege engines, arches, roads) | |
| Political history | |
| Strategy and tactics | |
| Infantry tactics | |
| Frontiers and fortifications (limes, Hadrian's Wall) |
A castellum is a small Roman detached fort or fortlet used as a watch tower or signal station. The Latin word castellum is a diminutive of castra ("military camp"), which in turn is the plural of castrum ("watchpost"); it is the source of the English word "castle".
The term castellum was also used to refer to a settling or storage reservoir along the length of an aqueduct.