when did humans start keeping track of time
History of timekeeping devices The oldest known sundial is from Egypt; it dates back to around 1500 BC (19th Dynasty), and was discovered in the Valley of the Kings in 2013.[11] Sundials have their origin in shadow clocks, which were the first devices used for measuring the parts of a day.[12] Ancient Egyptian obelisks, constructed about 3500 BC, are also among the earliest shadow clocks.[6][13][14]