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The Babylonian calendar was a lunisolar system. It used 12 lunar months per year, with months starting at the first visible crescent moon. Each month lasted 29 or 30 days. The lengths alternated in a pattern (often 30, 29, 30, 29, etc.) to give an average close to the lunar cycle of 29.5 days.
A standard year had about 354 days. To align with the solar year (about 365 days) and keep seasons in place, an extra month was added in certain years (leap years). From around the 5th century BCE, a regular 19-year cycle (Metonic cycle) was used, with 7 intercalary months over 19 years. The extra month was usually a second Adaru (Adar II), but sometimes a second Ululu (Elul II).
Babylonian Months and Approximate Gregorian Dates
The dates below are approximate and vary slightly each year due to lunar observation. They align Nisannu with the spring equinox (around March/April).
| Month | Approximate Gregorian Dates | Length (Days) |
|---|---|---|
| Nisannu (Nisan) | March 21 – April 20 | 30 |
| Ayyaru (Iyyar) | April 21 – May 20 | 29 |
| Simanu (Sivan) | May 21 – June 20 | 30 |
| Du’uzu (Tammuz) | June 21 – July 20 | 29 |
| Abu (Av) | July 21 – August 20 | 30 |
| Ululu (Elul) | August 21 – September 20 | 29 |
| Tashritu (Tishri) | September 21 – October 20 | 30 |
| Arahsamnu (Marchesvan) | October 21 – November 20 | 29 |
| Kislimu (Kislev) | November 21 – December 20 | 30 |
| Tebetu (Tevet) | December 21 – January 20 | 29 |
| Shabatu (Shevat) | January 21 – February 20 | 30 |
| Adaru (Adar) | February 21 – March 20 | 29 |
| Second Adaru (Ve-Adar or Adar II) (leap years) | March 21 – April 19 | 29 |
Leap year addition: Second Adaru (Adar II) — 29 or 30 days (added after Adaru to sync with solar year).
Note on lengths: Sources show a common alternation (30-29-30-29-…), but actual lengths depended on moon observation or later calculation. The pattern ensured an average month of ~29.5 days.
Cultural and Seasonal Significance of Each Month
- Nisannu — Start of the year. Celebrated the Akitu festival (New Year), renewal of agriculture, and cosmic order.
- Ayyaru — Time for maintenance, construction, health rituals, and purification.
- Simanu — End of grain harvest, focus on fertility and agricultural rites.
- Du’uzu — Named after god Tammuz. Mourning rituals for his death, linked to summer dryness.
- Abu — Continued mourning themes, prayers for rain and fertility return.
- Ululu — Preparation for New Year. Purification, repentance, reflection.
- Tashritu — Autumn start, end of harvest. Festivals to thank gods and seek blessings.
- Arahsamnu — “Month of rest” after harvest. Quiet period for recovery.
- Kislimu — Winter onset. Rituals for light return, solstice themes.
- Tebetu — Coldest month. Protection rites against evil, growth of light.
- Shabatu — Tree blooming, agricultural preparations, blessings for planting.
- Adaru (and Second Adaru in leap years) — Similar rituals, ensured cycle continuity.
Major Festivals: Akitu and Zagmuk
Akitu and Zagmuk are related but distinct. Many sources treat them as equivalent or closely connected, both celebrating Marduk’s victory over chaos (from Enuma Elish).
- Akitu (main New Year festival)
- Held in Nisannu (spring, March/April).
- Lasted 11–12 days.
- Focused on agricultural renewal, barley sowing, king’s divine mandate renewal.
- Included processions of god statues, Enuma Elish recitation, temple rites at Esagila, king’s humility ritual (stripped and reinstated), sacrifices, feasts.
- Zagmuk (“beginning of the year”)
- Older Sumerian name, often linked to winter solstice or New Year themes.
- Some texts place it in Kislimu/Tebetu (winter), but most evidence ties the main New Year celebration to spring (Nisannu).
- Celebrated Marduk’s triumph over Tiamat/chaos, renewal of order and light.
- Similar rituals: processions, recitations, king’s role, feasts.
- In practice, Zagmuk and Akitu refer to the same core spring festival in Babylonian times.
The calendar balanced lunar cycles with solar seasons through careful intercalation. This system influenced later calendars, including the Jewish one.
