oppidum

Oppidum, oppidi, n., second declension. The ordinary word for a walled town, and Caesar's default: urbs he keeps for Rome and for cities of real weight, civitas means the community of citizens rather than the bricks, and vicus is a village with no defences. If a Latin text says oppidum, picture walls.

The etymology is disputed, though ob plus the root of pes, "the place where you plant your feet, a stronghold", is the usual guess. Inhabitants are oppidani. One thing to watch: oppido as an adverb means "utterly, very much" and has nothing whatever to do with towns - it is a separate word that happens to look like the dative and ablative. Nothing survives in English, but plenty of European place names are oppida underneath.