As well as counting in 12s, they also measured time in 12s. Egyptian sundials, made 3,500 years ago, divided the day into 12 parts. Astronomers observed that the Moon had 12 cycles a year and 12 stars rose at regular intervals during the night. This led them to divide the night into 12 parts. Our 24-hour clock comes directly from the Egyptian system of splitting night and day into two sets of 12 hours.