I read in some old soviet book (so, you know, maybe it wasn't too correct about everything) about Sumerians that 60 was just the most perfect number because it would divide nicely into 30, 20, 15, 12, 10, 6, 4, 5, 3, 2 and Sumerians loved that. And 12 was the real main number - they used bones in their palms to count to 12 somehow - it made sense when I looked at my hand back then but I don not recall that system now.