Calendar, Babylonian

Babylonian Calendar: the first calendar to use the "Cycle of Meton".

Like all other calendars, the Babylonian calendar had twelve lunar months (about 354 days) and a problem to make these fit the solar year (about 365 days). In the western calendar, this is solved by disconnecting the lunar phase from the calendar month; the Babylonians found a different solution by adding leap months. In the table below, you will find the names of the Babylonian month and two calendars that were inspired by the Babylonian example.

 
Babylonian
Jewish
Persian
Julian calendar
 
I
Nisannu
Nisan
Adukanaiša
March/April
Harvest onions
II
Ajaru
Iyyar
Thûravâhara
April/May
Harvest; sowing sesame
III
Simanu
Sivan
Thâigaciš
May/June
Harvest flax and lentils
IV
Du'ûzu
Tammuz
Garmapada
June/July
Harvest chickpeas
V
Âbu
Ab
Turnabaziš
July/August
Planting millet
VI
Ulûlu
Elul
Karbašiyaš
August/September
Sowing chickpeas
VII
Tašrîtu
Tishri
Bâgayâdiš
September/October
Harvest sesame
VIII
Arahsamna
Marheshvan
Markâsanaš
October/November
Sowing broad beans and flax
IX
Kislîmu
Kislev
Âçiyâdiya
November/December
 
X
Tebêtu
Tebeth
Anâmaka
December/January
Sowing onions
XI
Šabatu
Shebat
Samiyamaš
January/February
Sowing
XII
Addaru
Adar
Viyaxana
February/March
Harvest broad beans

Originally, the king decided which month had to be added ("intercalated"), and when. Because this happened ad random, this was not very satisfying, and the Babylonian astronomers ("Chaldaeans") started to look for some kind of regularity. The key was the discovery, in the mid-eighth century, that 235 lunar months are almost identical to 19 solar years. (The difference is only two hours.) The Chaldaeans concluded that seven out of nineteen years ought to be leap years with an extra month. From now on, intercalary months were still announced by the king, but he was advised by an astronomer. After Babylon had been captured by the Persian king Cyrus the Great in 539, priestly officials took over. The Chaldaeans now started to look for a standard procedure for the intercalation of months. It was introduced in 503 BCE by Darius I the Great (if not earlier).

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
 
 
A
 
 
A
 
A
 
 
A
 
 
A
 
 
U
 
A

As this table shows, there are six years when a second month Addaru is added, and one year with an extra Ulûlu. The result is that the first day of the month Nisannu (New Year's Day) was never far from the vernal equinox (the first day of spring), so that the civil calendar and the seasons were never out of step. This system is often called the "Cycle of Meton", after an Athenian astronomer who introduced this system in the West. It is still used in the Jewish calendar and the Christian paschal computus.

At an unknown moment in the fourth century BCE, an even better procedure for the intercalation of months was invented. This time, a cycle of 76 years was used, one day was left out, and the limits of variability in the start of the year were further narrowed. The new system was already known in 331, because in that year the Macedonian conqueror Alexander the Great captured Babylon and ordered the Astronomical Diaries to be translated into Greek. The new knowledge was immediately applied in Greece: the astronomer Callippus of Cyzicus, a pupil of the philosopher Aristotle of Stagira, recalculated the length of the lunar month and proposed a new calendar, in which he applied the longer cycle. His new era, which was used by later Greek astronomers, started on 28 June 330, eight months after the capture of Babylon.

One final remark: the Babylonians did not develop a calendar era until the last years of the fourth century. It was only then that people started to date with formulae like "in the Nth year of the Seleucid era". Until then, regnal years were used, and it was very important to use the name of the correct king. In the Diadochi Chronicle, we find the charming piece of information that the Macedonian general Seleucus I Nicator, after he had expelled his rival Antigonus Monophthalmus, "declared that Year 7 of Antigonus-the-general had to be counted as Year 6 of Alexander, son of Alexander, and Seleucus-the-general."

Thanks...

... to Kelley Ross for the little pictures of the cuneiform signs.

This page was created in 2004; last modified on 27 July 2015.