Egyptian 365-Day Civil Calendar

The ancient Egyptians developed the world's first known calendar based on a 365-day solar year, a revolutionary innovation that provided consistency for administrative, agricultural, and religious purposes. The civil calendar consisted of twelve 30-day months organized into three seasons (Akhet/Inundation, Peret/Emergence, and Shemu/Harvest), plus five additional epagomenal days dedicated to the birthdays of major deities. This calendar was synchronized with the heliacal rising of Sirius (Sopdet) which coincided with the annual Nile inundation, though without leap years the calendar gradually shifted through the seasons over time, completing a full cycle every 1,460 years (Sothic cycle).