The various regions of ancient Greece had different calendars. Those of Athens, Delos, Delphi, Crete, Ionia, Cyprus, Macedonia and others, are known. The most important and best known is the Athenian calendar. The Athenians initially followed a lunisolar year based on the combined movements of the sun and the moon. A year consisted of 12 lunar months beginning and ending with the moons. Now, as one lunar month is approximately 29 1/2 days, each month consisted alternatively of 29 and 30 days. The first were hollow months and the second full months, as in the Jewish calendar. The first day of each month corresponded to the appearance of the crescent moon, similar once again to the Jewish system. The Athenian calendar consisted initially of 12 and later 13 months, named as follows: 1. Hekatombaion: 30 days 2. Metageitnion: 29 days 3. Boedromion: 30 days 4. Pyanepsion: 29 days 5. Maimakterion: 30 days 6. Poseidon I: 29 days 7. Poseidon II: 30 days 8. Gamelion: 30 days 9. Anthesterion: 29 days 10. Elaphebolion: 30 days 11. Munychion: 29 days 12. Thargelion: 30 days 13. Skirophorion: 29 days Poseidon II was the intercalary month. In other periods, the first, third, fourth, sixth, seventh, ninth and eleventh months had 30 days and the others 29. The Greeks did not use weeks. They divided their months into three phases of 10 days each. In months consisting of 29 days, the third period numbered only nine days. The first day was called Noumenia to mark the start of the month from where the days were numbered up to 10. The days of the second 10-day phase were similarly numbered as days above 10, or middle days; finally the days above 20 were numbered from 1 to 9 or 10, or counted down from 10 or 9, 8, 7 and so forth to conclude the month. The final day of the month was called "the old and the new" because the lunar month consisted of 29 1/2 days so the last day could be regarded as belonging in part to the concluding month and in part to the incoming month. The day began in the evening at dusk; the diurnal part and nocturnal part together were called nychthemeron. A year of 12 lunar months consisted of 354 days and 8 hours. It far from matches a solar year of 365 days 5 hours and 48 minutes. To bring the lunar months and solar year into line with one another, the Greeks - like other peoples - resorted to intercalating a 13th month, which gave years of 354 or 355 days and others of 383 or 384 days. The eight-year cycle, or octaeteris, appears to have been introduced by Solon to adjust the succession of different years. The octaeteris consisted of 5 ordinary years of 354 days and 3 intercalary years of 13 months, the thirteenth of which, known as an embolismic month, was 30 days long, equalling in all 2,922 days. Now, eight solar years only consist of 2,921 days 22 hours and 30 minutes whereas 99 lunar months totalled 2,923 days 12 hours and 40 minutes, in other words a difference of around 1 1/2 days. The idea was then conceived of doubling the octaeteris to 16 years instead of 8, and of intercalating 3 additional days to replace 3 months of 29 days with 3 months of 30 days. This change restored the balance between the calendar and the moon, but misaligned it once again with the sun! It was then that the celebrated astronomer Meton devised in 432 BC the famous Metonic cycle named after him. The basis of the cycle is the sum of 235 lunar months or 6,940 days, equivalent to 19 solar years of 365 + 5/19 days. When Meton announced his discovery at the Olympic Games, the Athenians were so enthusiastic that they had the formula engraved publicly in gold letters, hence the term "golden number" assigned to each year in sequence to indicate its position in the nineteen-year cycle. For all its gold, the Metonic cycle was still not perfect. At the end of 19 years, the calendar lagged 7 hours behind the moon and 9 hours behind the sun. Bringing their movements into alignment was no easy matter. Calippus, in turn, attempted to do so. Assuming the delay to be equivalent to a quarter of one day, he multiplied the Metonic cycle by 4, which gave a period of 76 years. He deducted 1 day from this period, known as the Callippic cycle. At the end of this period, the calendar was aligned with the sun but was still 5 hours behind the moon! To correct this difference, Hipparchus deducted 1 day from 4 Callippic cycles, i.e. 304 years. The Athenian year first began at the winter solstice and subsequently at the summer solstice. The calendar year began with the new moon following the summer solstice and marked the first day of the first month. Initially, only two seasons - hot and cold - were distinguished. Later on, four seasons were established on the basis of the appearance of certain stars. Greece is the homeland of the celebrated calendar epoch of the Olympiads, or period of four years, named after the games were held at Olympia every four years. The first year of the Olympiad era dates back to 776 BC. Greek calendars remained in use until the time of the Roman conquest. After the Julian reform, the Greeks gradually adopted the Roman calendar, although they initially retained their own dates for the start of each year and, in general, their own names for each month. However, some were replaced by the names of Roman emperors.