Blame it on the Babylonians. They used base 12 for mathematics rather than base 10 as we do. They saw numbers such as 6, 12 and 60 as round numbers as we do 5, 10, 100, etc. This was primarily because they divided the sky into 12 sections for the Zodiac constellations, therby dividing a circle into 360 parts (degrees) which divided the year into twelve months and the day into 12 hours and the night with 12 hours as well. The hours were further divided into 60 minutes with 60 seconds each.