Around 5,000 years ago, the Sumerians in the Tigris-Euphrates valley (today’s Iraq) appear to have had a calendar, but it is unknown if they truly had a timekeeping device. The Sumerians divided the year into months of 30 days; the day was divided into 12 periods (each corresponding to two of our modern hours) and the periods into 30 parts (each corresponding to four of our minutes).

Overall, most researchers agree that the Egyptians were the first serious timekeepers. Around 3500 B.C.E., they erected obelisks (tall, four-sided monuments), placing them in specific places in order to cast shadows as the Sun moved overhead. This thus created a large, crude form of a sundial. This sundial time was broken into two parts: before and after noon. Eventually, more divisions would be added, breaking down the time units even more into hours. Based on the length of the obelisks’ shadows, the huge sundials could also be used to determine the longest and shortest days of the year.