Since the first recordings of civilization magic existed. It is the unexplainable or in other terms: Everything that science fails to explain. Every civilizations progresses by taking bits of what they called magic and explained it until it becomes science. Those who progress further, or never bothered at all, discover that there truly is a core of unexplainable phenomenons that just work. Be it seemingly simple words that produce unbelievable or runes of power that changes material even the best smith can't explain, every civilization sooner or later learns of it.
Historically fascinating is that usually the less scientific progress a civilization has, the more understanding they have of magic, and when they develop their science, they usually distance themselve more and more from their magical heritage until there are only tales of arch-mages and massive magical structures left.