When was the idea of "three" wise men made official?

the bible never says three- i am sure there were many more. saying Christ received gifts of gold, frankincense and myrrh is like saying i received gifts of books, clothes and trinkets. that does not mean that is all i got or three people gave them to me- it is more like a summary. so when was it officially decided that there were only three- or is it simply easier and cheaper to make Nativity sets that way?