Castellum
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A castellum<ref>Charlton T. Lewis, Charles Short, A Latin Dictionary</ref> in Latin is usually:
- a small Roman fortlet or tower,<ref>C. Julius Caesar, Gallic War; 2,30</ref> a diminutive of {{#invoke:Lang|lang}} ('military camp'), often used as a watchtower or signal station like on Hadrian's Wall. It is distinct from a {{#invoke:Lang|lang}}, which is a later Latin term that was used particularly in the Germanic provinces.
- a distribution, header and settling tank in a Roman aqueduct or castellum aquae.
It is the source of the English word "castle".