Ancient Greece > AthensPericlean Citizenship Law
Ancient Athenians, for a time, profoundly feared extending privileges of citizenship. To avert this disaster they passed the Periclean Citizenship Law (451/450 B.C.) reserving the right of legitimacy only to children born of two Athenian citizens. Both parents had to be astos to confer citizenship on their children. If they weren't astoi, they might be resident aliens -- known as metics, or foreigners (xenoi).
Pericles was the leader of Athens at the time, but he suffered from this law by being prevented from marrying Aspasia. Aspasia was not from Athens, but Miletus, and so was metoikos, not astos.