Early Greek Calendars

Like Romans in the middle of the 5th century B.C., some Greek states also made use of an intercalary month every second year at that time. 1  Here’s a quote from Herodotus, “the father of history:”

“I put the boundary of human life at seventy years. These seventy years have twenty-five thousand two hundred days, not counting the intercalary month; but if every other year be lengthened by a month so that the seasons come out right, these intercalary months in seventy years will be thirty-five, and the days for these months ten hundred and fifty. So that all the days of a man’s life are twenty-six thousand two hundred and fifty…” 2

Herodotus’ statement above is deciphered on the right. It indicates that during his lifetime (mid 5th century B.C.) the Greek calendar with which Herodotus was familiar had 12 months of 30 days each plus an intercalary month, also of 30 days, added every second year.
So the total number of days in two calendar years was 750 days then as compared with only about 730½ days in two solar years at the present time.

25,200 days ÷ 70 years = 360 days per year (not counting the intercalary month added every other year).
The days for intercalary months were 1,050 days ÷ 35 months = 30 days a month.

It’s interesting that Herodotus believed an average length of 375 days kept their calendar in step with seasons. Many modern historians have questioned that statement. They reason that average calendar year length would be off by only a little over five days in a year of twelve 30-day months without the intercalation Herodotus claimed, as compared with being off by almost ten days with it.
But according to Sir Thomas Heath (when writing about Greek astronomy) Geminus also said “The ancients added the intercalated month every other year.” 3
A modern writer, E. J. Bickerman, claimed they rounded off the length of each two months to a total of 59 days and intercalated a 29-day month every two years. That would have made the average length of a Greek lunisolar calendar year 368½ days. Nevertheless, he said, “Greek cities…and the Romans as well…were satisfied with this device.” 4
It’s quite possible that Bickerman was referring to a time period other than when Herodotus lived. But how could Greek states have been satisfied with intercalation that was almost ten days too long (according to Herodotus) or over 3 days too long (Bickerman)?
The calendar year-length problem was resolved when the Metonic Cycle was discovered and subsequently used to determine intercalation requirements. You can read about many nation’s calendar corrections around that time at 8th to 4th Century B.C. Calendar Changes

And you can find lots about the father of history by going to Herodotus on the Web.

(1) Bickerman, Elias Joseph. Chronology of the Ancient World.
Ithica, New York: Cornell University Press, 1968. pp. 44-45.
(2) Herodotus. The History. (5th century B.C.)
Translated by David Grene. Chicago & London:
The University of Chicago Press, 1988. Book 1, Chapter 32.
(3) Heath, Sir Thomas L. Greek Astronomy. 1932.
(Quote from Geminus.) (8,3)
(4) Bickerman. op. cit. p. 27.