1. Mayan Calendar
This ancient calendar was used by the Maya civilization in Mesoamerica from around 2000 BCE to 1500 CE. The Mayan calendar is considered one of the most complex calendars due to its interlocking cycles, which included multiple levels of time-keeping and symbolic meaning. The Mayan calendar consisted of three main cycles: the Tzolkin (260 days), the Haab (365 days), and the Long Count (varied lengths). According to legend, the Mayan calendar was considered so complex that it required a special priest called an ahau to interpret its meanings.
2. Roman Calendar
The ancient Roman calendar was introduced in 753 BCE and was initially based on a lunar cycle. However, due to inconsistencies and errors, the Romans had to add or remove months periodically to keep the calendar aligned with the solar year. The Roman calendar is considered complex because of its irregularities and lack of standardization. In 45 BCE, Julius Caesar introduced the Julian calendar, which reformed the Roman system but still contained some complexities.
3. Babylonian Calendar
The Babylonians used a lunisolar calendar from around 1800 BCE to 539 CE. This calendar was based on the cycles of the moon and sun, resulting in irregular months that shifted throughout the year. The Babylonian calendar is considered complex due to its use of two main cycles: the month and the year. Each month had either 29 or 30 days, with an additional 13th month added every few years to keep the calendar aligned with the solar year.
4. Egyptian Calendar
Ancient Egypt used a 365-day calendar from around 2500 BCE to 391 CE. This calendar consisted of 12 months, each beginning with the first day of the new moon. The Egyptian calendar is considered complex due to its use of multiple cycles and symbols for time-keeping. Additionally, the Egyptians made adjustments every three years by adding an extra month called "Epagomeni".
5. Persian Calendar
Introduced in 625 CE, the Persian calendar was used under various dynasties until the advent of the Islamic calendar. The Persians combined lunar and solar cycles to create a complex system that is still used today. Each year consists of 12 months, with each month beginning on the first sighting of the new moon. Although this calendar has several complexities, its simplicity lies in its consistent cycle.