The number 12 was hugely important to the people of Ancient Egypt. As well as counting in 12s, they also used it to mark the passing of time. Egyptian astronomers observed that the Moon had 12 cycles a year. The earliest-known sundials, made 3,500 years ago, divided the day into 12 parts. The 24 hour clock we use today comes directly from the Egyptian system of splitting night and day into sets of 12 hours.