Wikipedia
Municipium (pl. municipia) was the Latin term for a town or city. Etymologically the municipium was a social contract between municipes, the "duty holders," or citizens of the town. The duties, or munera, were a communal obligation assumed by the municipes in exchange for the privileges and protections of citizenship. Every citizen was a municeps.
The distinction of municipia was not made in the Roman kingdom; instead, the immediate neighbors of the city were invited or compelled to transfer their populations to the urban structure of Rome, where they took up residence in neighborhoods and became Romans per se. Under the Roman Republic the practical considerations of incorporating communities into the city-state of Rome forced the Romans to devise the concept of municipium, a distinct state under the jurisdiction of Rome. It was necessary to distinguish various types of municipia and other settlements, such as the colony. In the early Roman Empire these distinctions began to disappear; for example, when Pliny the Elder served in the Roman army, the distinctions were only nominal. In the final stage of development, all citizens of all cities and towns throughout the empire were equally citizens of Rome. The municipium then simply meant municipality, the lowest level of local government.
Usage examples of "municipium".
Jerusalem gleamed in the westering sun, Sextus noticed a slave of the municipium who wrote down the names of individuals who came and went.
After the citizenship was made universal for all the peoples of the Italian Peninsula, a municipium principally meant a town and its district which had retained some of its self-governing powers, and still owned its public lands.
Many other passages of Tertullian prove that the army was full of Christians, Hesterni sumus et vestra omnia implevimus, urbes, insulas, castella, municipia, conciliabula, castra ipsa.