Sumerian and then Babylonian mathematics counted in base sixty, and the choice was not arbitrary. Sixty has twelve divisors, 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30 and 60, and no smaller number has as many. In a system without decimal fractions, that divisibility is the whole game: a third, a quarter, a fifth, a sixth of sixty are all whole numbers, whereas in base ten a third is a repeating fraction.
The consequences are still in use. Sixty seconds to the minute, sixty minutes to the hour, and 360 degrees in a circle are Babylonian, transmitted through Greek astronomy, Ptolemy computed in sexagesimal fractions, and thence to Arabic and Latin science and to us. The words minute and second come from the Latin pars minuta prima and pars minuta secunda, the first and second small parts of a degree. No other feature of Babylonian civilisation has survived so completely.
The 360-degree circle follows from the same base, helped by the convenient near-coincidence that a year is roughly 360 days, Babylonian schematic calendars used twelve months of thirty days for administrative purposes while the real calendar was lunisolar and intercalated.
Why the Sumerians chose sixty is not settled. Proposals include a merger of two earlier systems using five and twelve, and finger-counting methods using the twelve finger joints of one hand against five fingers of the other. The evidence for either is indirect. What is certain is the mathematical advantage, and it is enough to explain why the system was kept for three thousand years.