12 is a very practical number. Unlike 10, which you can only divide by 2 and 5, you can divide 12 by 2, 3, 4 and 6. When you have not yet invented the decimal system and are doing fractions instead, being able to divide something by a lot of other numbers is very very practical.
24 is also pretty practical, much more practical than 25 or 20. 25 can only be divided by 5, and 20 can only be divided by 2, 4, 5 and 10. 24, on the other hand, can be divided by 2, 3, 4, 6, 8 and 12.
60 is another such practical number. Unlike 50 (divisible only by 2, 5, 10, and 25), 60 can be divided by 1, 2, 3, 4, 5, 6, 10, 12, 15, 20 and 30.
360, well, the same thing again: you can divide it by 1, 2, 3, 4, 5, 6, 8, 9, 10, 12, 15, 20, 24, 30, 45, 60, 90, 120, and 180.
So if you live in a society which not yet have invented the decimal system, and had to be using fractions, these numbers were very practical.
As you have noticed, at least 12 is associated with circles, the numbers of a clock face. Well, so are the others, specifically 24 (hours from mid-day to mid-day) and 360 (degrees of a circle).
It is no accident. Nature is full of circles, including the sky, and these numbers are very well suited for circular things. So when the Babylonians and Sumerians started to describe things that move in the sky, they used these numbers to do it.
They rounded a bit, for instance about the year which they realised was not perfectly 360 days, but 365. A common way for ancient civilisations was to have a five day party when you reached the end of the year. The Moon’s cycle was not perfectly 30 days. Depending on if you thought that the constellations and sun were more important than the Moon, you rounded by just declaring months to be 30 days, or you inserted a “leap month” every other year or so.
So that’s where you have the zodiac from as well: people associated patterns of stars to gods and monsters in their legends, and constructed belt of 12 of them across the cosmic equator. They are not perfectly aligned or evenly spread out, but close enough to still squeeze them into the number 12. These could then be used to tell which month you were in (if you thought that the sun and constellations were more important than the Moon cycle).
Credit : Quora
Picture Credit : Google