What is "trittys"

Trittyes ( Ancient Greek: τριττύες; singular trittys (τριττύς)) were population divisions in ancient Attica, established by the reforms of Cleisthenes in 508 BC. The name means "thirtieth," and there were in fact thirty trittyes in Attica. Each tribe, or phyle of Athens was composed of three trittyes, one from the coast, one from the city, and one from the inland area. Trittyes were composed of one or more demes; demes were the basic unit of division in Attica.