Castellum
From Infogalactic: the planetary knowledge core
Lua error in package.lua at line 80: module 'strict' not found. Lua error in package.lua at line 80: module 'strict' not found.
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.