Castellum

Reconstructed Limes watchtower, between Bad Nauheim and Pfaffenwiesbach, Germany.

A castellum in ancient Latin is usually either:

• a small Roman fortlet or tower, a diminutive of castrum ("military camp"), often used as a watchtower or signal station e.g. on Hadrian's Wall. It should be distinguished from a burgus, which was a later Latin term used particularly in the Germanic provinces.

• a settling or storage tank in a Roman aqueduct or it:castellum aquae.

It is the source of the English word "castle".

Ruins of the castellum divisorium in Nîmes, France, which distributed water from an aqueduct to individual water pipes.