"Long before" and "commonly" is a matter of perspective. It was first struck as coins about 2700 years ago, and was definitely used as money in a few countries at least 300 years earlier, and possibly as much as 3000 years earlier. There is no evidence to suggest that it was in wide use as money until about 2200 years ago, only in a few places like the Mediterranean. Then again, maybe there wouldn't be, since not many places had writing.
Coinage really just seems to be a technology improvement to make trade more efficient, because you can more quickly verify and count the units.