The ancient Egyptians developed the first known calendar around 3000 BC.

The Egyptian calendar was used for religious festivals, agricultural planning, and tax collection.

The Egyptian calendar had 365 days in a year.

The extra day added to the Egyptian calendar every four years was called the Epagomenal day.

The Babylonians developed a calendar based on a 360-day year.

The Babylonian calendar was a lunisolar calendar, meaning it was based on both the solar year and the lunar month.

The Babylonian calendar had 12 months in a year.

The extra month added to the Babylonian calendar every few years was called the Intercalary month.

The Mayans developed a calendar based on a 260-day year.

The Mayan calendar was a solar calendar, meaning it was based on the solar year.

The Mayan calendar had 18 months in a year.

The Mayan calendar did not have an extra day added every four years.

The Chinese developed a calendar based on a 365.242-day year.

The Chinese calendar was a lunisolar calendar, meaning it was based on both the solar year and the lunar month.

The Chinese calendar had 12 months in a year.

The extra month added to the Chinese calendar every few years was called the Intercalary month.