The development of the Calendar started around 4000 BC. Originally, the calendar was a moon based one, using the moon phases as a basis. Then, in around 2000 BC, the Egyptians decided that they needed a better calendar, which brought us a new sun-based calendar. While most used this new calendar, others still used the older lunar calendar. The only improvement that the calendar needed was the addition of leap years, which were added later.

The Egyptian 365-day calendar was very simple, 365 days. In these 365 days were 12 months, each with 30 days, and 4 seasons throughout the year. There was also an extra 5 day month to celebrate the birthdays of the gods. On the complex side of things, the calendar was designed around the rising of the star Sothis, which was sun based. They counted the number of days between each rise of the sun-based star to figure out the length of a year. 

The calendar was important for mainly agricultural reasons. In fact, the calendar was made specifically to track when the Nile River flooded. Basically, when the Nile flooded, it left behind a lot of fertile black mud that we call silt. It was important to know when the annual flooding of the Nile occurred as the event was crucial for any agricultural work. The calendar was also used for administrative purposes, which allowed for efficient management of resources, labor, and taxation across the empire.

The calendar had a massive impact on today, as it basically influenced the current, modern calendar. It only needed a couple of revisions, such as the addition of leap years by Julius Caesar in the Julian calendar. Also, while it was very similarly structured, there were differences, such as the names of the days and months, as well as the fact that the days don’t line up with the current calendar. However, the revised Julian calendar would end up contributing to the development of today’s calendar, or the Gregorian one.