civitas

thumb|300px|A Roman military diploma, or certificate of successful military service, granting citizenship to a retiring soldier and the dependents he had with him at the time. The key phrase is "est civitas eis data" where means "citizenship".

In Ancient Rome, a ' (; plural '), sometimes translated as "city", was the social body of the , or citizens, united by their laws, which gave them responsibilities () on the one hand, and rights on the other. The agreement () has a life of its own, creating a or "public entity" (synonymous with ), into which individuals are born or accepted, and from which they die or are ejected. The is not just the collective body of all the citizens; it is the contract binding them all together, because each of them is a .