Around 3,500 BCE (a long, long time ago), the Egyptians used the shadows the giant stone obelisks cast on the ground to tell the time of day. Each obelisk was built to tell a story. But they worked very well as shadow clocks. Later on, the ancient Egyptians invented the first portable timepiece.

Yes, obelisks were among the earliest timekeeping devices used by ancient civilizations, functioning essentially as giant sundials or gnomons. As early as 3500 BCE, ancient Egyptians built these slender, four-sided monuments to track the sun's movement throughout the day. By observing the length and direction of the shadow cast by the obelisk, people could divide the day into specific segments, such as morning and afternoon. They were also used to mark significant astronomical dates; for example, the shadow at noon reached its shortest point during the summer solstice and its longest during the winter solstice. Later versions often featured markers or subdivisions around the base to provide more precise "hour" measurements. Beyond their practical utility for agriculture and religious scheduling, obelisks served as powerful symbols of the sun god Ra, physically connecting the terrestrial world to the celestial rhythms of the cosmos through the constant, predictable movement of light and shadow across the desert landscape.