municipal (adj.) [...] from Latin municipalis "of a citizen of a free town, of a free town," also "of a petty town, provincial,"
from municipium "free town, city whose citizens have the privileges of Roman citizens but are governed by their own laws,"
from municeps "citizen, inhabitant of a free town."
[Of municeps:] Second element is root of capere "assume, take" (see capable).
First element is from munus (plural munia) "service performed for the community, duty, work," also "public spectacle paid for by the magistrate, (gladiatorial) entertainment, gift,"
from Old Latin moenus "service, duty, burden,"
[PIE 1.] from PIE *moi-n-es-, generally taken as a suffixed form of root
*mei- (1) "to change, go, move" (Watkins; see mutable);
[PIE 2.] but Tucker says "more probably" from the other PIE root *mei- meaning "bind,"
so that munia = "obligations" and communis = "bound together."
The etymology above suggests that only certain Roman citizens were bound to moenus. So besides the young, sick, and old, were there other citizens who lacked any such moenus?
For example, if you lived outside a city, were you excepted from moenus?