What is the basis for modern timekeeping?

Modern society has adopted a 365-day solar calendar with a leap year occurring every fourth year (except century years not evenly divisible by 400). The modern clock is based on the number 60. In about 3000 B.C.E. the Sumerians used a base 10 counting system and also a base 60 counting system. The timekeeping system inherited this pattern with 60 seconds per minute and 60 minutes per hour. Ten and 60 fit together to form the notion of time: 10 hours is 600 minutes; 10 minutes is 600 seconds; 1 minute is 60 seconds.