They used base-60 'sexagesimal' fractions — which is why we have 60 minutes in an hour.
Babylonians chose base 60 because it has many divisors (1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30, 60), making fractions clean. 1/3 is exactly 20/60 with no repeating decimal. We inherited their system for measuring time and angles.
