Two Years Running at Once

Twelve lunar months run to roughly 354 days, eleven days short of the solar year, so left uncorrected the festival calendar would cycle through the seasons over the span of a generation, putting a harvest festival in midwinter within thirty years. Athens corrected for this by inserting an intercalary month, but did so irregularly rather than by a fixed rule until the astronomer Meton proposed a nineteen year cycle of intercalation in 432 BCE, a scheme later associated with his name as the Metonic cycle and adopted only unevenly by the Athenian state rather than enforced as binding civic law. To complicate matters further, Athens ran a second, separate reckoning for its administrative business, the conciliar year tied to the terms of the Council rather than to the festival months, and the two systems frequently diverged, so that an Athenian document might carry a date that made sense administratively while conflicting with where the festival calendar actually stood that month.

No single complete official fasti comparable to Rome's pontifical calendar survives from Athens. What is known of the Attic calendar comes from inscribed public decrees that dated themselves by month and sometimes by festival, from later Hellenistic and Roman era grammarians who had to explain month names their own readers no longer used, and from literary references that mention, in passing, when a particular festival fell.