Within Athens, they played a prominent role in social and religious life, particularly in the major festival called the Apatouria.
[1] Particularly in anthropology, the term is also applied to similar descent groups of multiple clans in other societies.
It is possible that they are Ionian in origin and that their presence in Athens stems from a known migration from Ionia in the late Mycenaean period.
The existence of the Apatouria in both Ionia and Athens complicates the second theory of origin somewhat, but at present scholars are highly uncertain about how phratries actually emerged.
It is known that he reorganized and reconstituted the phylai and created the demes, two other groups to which all Athenian citizens belonged.
Lambert, speculates that the phratries were not involved in the military or political life or responsibilities of citizenship and that Cleisthenes only reorganized institutions in those areas.
He further speculates that any change that did occur in the phratries was a reaction to the reorganization of other Athenian institutions rather than a reform undertaken directly by Cleisthenes.
[1] Phratries likely reached their peak importance in Athens between the 5th and 3rd centuries BCE, when we have the most extant records of them.
In this time, they played a prominent role in Greek religious and social life.
The sole known exceptions were naturalized citizens, who were usually enrolled in a phratry upon gaining Athenian citizenship.
Phratries became even more concerned with citizenship and parentage during the Peloponnesian War, when widespread migration, military service and premature death heightened the difficulty of record keeping.
[1] The biggest cache of surviving documents, the decrees of a phratry called the Demotionodai centered in a town called Decelea in northern Attica, date from this period and almost exclusively discuss membership qualifications and introduction procedures.
[citation needed] The Demotionodai decrees detail the scrutiny procedure for that phratry in the decades following the Peloponnesian War.
[1] The procedures are also very concerned with the introduction of candidates for phratry membership who do not have parents to vouch for their eligibility.
[1] The only reliable extant records of citizens without phratry membership also date to around the time of the Peloponnesian War.
Those same new citizens were also enrolled in phylai, which had been essentially dormant for centuries, although they technically still existed.
After 150 BCE, citizenship grants no longer include enrollment in phratries, demes or phylai.
Another related and complementary theory is that citizenship became more tightly linked to military service rather than descent, which had a similar effect on the phratries and their ceremonies of scrutiny and induction.