The text provides an extensive overview of the invention, evolution, and profound impact of ancient calendars across various civilizations. It begins by tracing the origins of timekeeping from early markings to the development of sophisticated systems like the Sumerian lunar calendar and the Ancient Egyptian solar calendar. The source details how different types of calendars―solar, lunar, and lunisolar (such as the Chinese system and the complex Maya calendars)―were devised through precise astronomical observation and mathematical calculation. Crucially, the document highlights the revolutionary influence of calendars on agriculture, demonstrating how systems like China's twenty-four solar terms guided rice cultivation, and how calendars managed the entire barley cycle in Mesopotamia. Finally, it explores the calendars' pervasive role in shaping society, ranging from regulating daily life and establishing the rhythm of religious festivals to serving as a core symbol of political legitimacy and centralized power for ruling authorities.