The Egyptian calendar was one of the earliest known calendars, developed by the ancient Egyptians around 3000 BCE. It consisted of 12 months, each with 30 days, followed by an additional 5 days known as epagomenal days. This structure created a year of 365 days, which was crucial for agricultural planning and religious festivals. To keep track of time, the Egyptians relied on the annual flooding of the Nile River, which marked the start of their new year. The calendar was primarily lunar, but the Egyptians also observed the solar year, leading to a system that was both practical and aligned with their environment.