Latin term for ‘fort’. Used for the smaller forts of the Roman Empire. The diminutive form of castrum. The frontiers of the Roman Empire had many castella as a line of defense. One of them is Levefanum near Wijk bij Duurstede, the Netherlands. This is in the same location as the early medieval trade town of Dorestad. For more information, see Livius.
A castellum aquae was a water reservoir in Roman times, where water would be distributed to fountains, public baths and houses. A wonderful site for more information is: Roman Aquaducts.