A second fundamental distinction is that between the citizens on the one hand, that is the politai, that part of the population that can take an active part in politics; and the
Non-citizens on the other. There exist poleis that divide the inhabitants into a group of “true citizens,” such as the Spartan Homoioi, and into a group of inferior citizens or even serfs or slaves. We are talking about the autochthonous population, not about foreigners or slaves supplied from elsewhere. The alternative is a polis that extends citizenship rights to all freeborn men on its territory. Such was the case in Athens. It is only those who came in at a later date who were excluded.
A citizen was a grown-up, freeborn man who satisfied certain criteria. In the Archaic period, mainly economic criteria were used: the amount of property owned and the contribution that one could make to the defense of the polis. In the Hellenistic period, there would be in many places a return to such economic criteria. In classical Athens, it was above all one’s lineage that decided whether one was a citizen or not. After 451-450 BC, a strict law stipulated that one could claim Athenian citizenship if one was a male born in legal wedlock of a father who was an Athenian citizen and a mother who was the daughter of an Athenian citizen. Also, the father had to recognize the child as a member of his oikos, his household, and it had to be registered with the polis. As long as they were minors, the sons of citizens could not exercise any of their citizenship rights, and thus were in a position comparable to that of women, who too could only claim to be related to a citizen. When the son attained majority on his 18th birthday, his citizenship came into effect. In the case of women, this never happened: in the eyes of the Athenians, they remained minors as long as they lived.
The best explanation for the strict rules on Athenian citizenship seems to be that the citizens did not want to dilute the important economic and political privileges that were part and parcel of their citizenship rights, by opening up the citizenship to outsiders. They wanted to restrict these privileges to a relatively small group. Only citizens could own immovable property, both land and a dwelling on one’s own land. Non-citizens were not allowed to own any part of the polis territory. Only citizens could inherit from other citizens, legally marry a citizen’s daughter, lease concessions in the Attic silver mines, be eligible for distributions of money or grain by the polis, hold public office and official priesthoods, take an active part in the political life of the polis, be a jury member in the courts, and join in the religious life of the polis to the full.
The polis was home to many free inhabitants who did not match the criteria for citizenship. Athens with its busy harbor was visited by many strangers, xenoi, who were passing through: traders, sailors, itinerant craftsmen, tourists, and mercenaries. Also, a large number of scholars came to Athens, which in the 4th century was an important intellectual center. But not everybody was a temporary visitor: there were also many immigrants who came to stay. They had fled poverty, warfare, or personal problems, or had been attracted by the economic potential of Athens. The last-mentioned group, the ones who stayed on, had their own clear juridical status. They were called metoikoi, “(im)migrants,” anglicized as “metics.” The only privilege that the metic status carried with it was the permission to live in Athens. In exchange for that privilege, one had to shoulder several duties: the payment of the metoikion, a poll tax or capitation, and serving in the Athenian army. No metic enjoyed the many citizen privileges already mentioned, and in addition metic and citizen were not completely equal before the law.