Babylonian Calendar

The Babylonian calendar was a lunisolar system. A year had 12 lunar months, and each month began when the first crescent moon was seen. A month lasted 29 or 30 days. The lengths often alternated (30, 29, 30, 29 and so on), which gives an average close to the lunar cycle of 29.5 days.

A standard year had about 354 days. The solar year has about 365. To keep the seasons in place, an extra month was added in some years (leap years). From around the 5th century BCE a regular 19-year cycle (the Metonic cycle) was used, with 7 extra months in every 19 years. The extra month was usually a second Adaru (Adar II), and sometimes a second Ululu (Elul II).

Babylonian months and approximate Gregorian dates

The dates below are approximate. They shift a little each year because each month depended on seeing the moon. The table starts Nisannu at the spring equinox (around March or April).

Leap year month: Second Adaru (Adar II), 29 or 30 days, added after Adaru to stay in step with the solar year.

Month lengths: Sources show a common alternation (30, 29, 30, 29 and so on). The real length of each month depended on watching the moon, and later on calculation. The pattern kept the average month at about 29.5 days.

What each month meant

• Nisannu: start of the year. The Akitu festival (New Year) was held, celebrating the renewal of farming and of cosmic order.
• Ayyaru: a time for repairs, building, health rituals and purification.
• Simanu: end of the grain harvest, with fertility and farming rites.
• Du’uzu: named after the god Tammuz. Mourning rituals for his death, linked to the dry summer.
• Abu: the mourning went on, with prayers for rain and the return of fertility.
• Ululu: getting ready for the New Year with purification, repentance and reflection.
• Tashritu: start of autumn and end of the harvest. Festivals to thank the gods and ask for blessings.
• Arahsamnu: the “month of rest” after the harvest, a quiet time to recover.
• Kislimu: start of winter. Rituals for the return of light, with solstice themes.
• Tebetu: the coldest month. Rites of protection against evil, and the growing of the light.
• Shabatu: trees blossom. Farm preparations and blessings for planting.
• Adaru (and Second Adaru in leap years): similar rituals, keeping the cycle going.

The great festivals: Akitu and Zagmuk

Akitu and Zagmuk are related but not the same. Many sources treat them as equal or closely linked. Both celebrate Marduk’s victory over chaos, from the Enuma Elish.

• Akitu (the main New Year festival)
  • Held in Nisannu (spring, March or April).
  • Lasted 11 to 12 days.
  • About the renewal of farming, the sowing of barley and the renewal of the king’s divine mandate.
  • Included processions of god statues, a recitation of the Enuma Elish, temple rites at the Esagila, the king’s humbling (stripped and then reinstated), sacrifices and feasts.
• Zagmuk (“beginning of the year”)
  • The older Sumerian name, often linked with the winter solstice or with New Year themes.
  • Some texts place it in Kislimu or Tebetu (winter), but most evidence ties the main New Year festival to spring (Nisannu).
  • It celebrated Marduk’s triumph over Tiamat and chaos, and the renewal of order and light.
  • The rituals were similar: processions, recitations, the king’s role and feasts.
  • In practice, Zagmuk and Akitu name the same spring festival in Babylonian times.

The calendar kept the lunar months and the solar seasons together through careful use of the extra month. The system shaped later calendars, including the Jewish one. See also the oldest calendars of the world and Babylon.