Sumerians Looked to the Heavens as They Invented the System of Time… And We Still Use it Today. One might find it curious that we divide the hours into 60 minutes and the days into 24 hours - why not a multiple of 10 or 12? Put quite simply, the answer is because the inventors of time did not operate on a decimal (base-10) or duodecimal (base-12) system but a sexagesimal (base-60) system. For the ancient Sumerian innovators who first divided the movements of the heavens into countable intervals, 60 was the perfect number. The number 60 can be divided by Arabic numerals 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, and 30 equal parts. Moreover, ancient astronomers believed there were 360 days in a year, a number which 60 fits neatly into six times. The Sumerian Empire did not last. However, for more than 5,000 years the world has remained committed to their delineation of time.
ETA: This is ex-FB. Someone in the comments takes issue with this theory/story, but it sounds good regardless.