It's not very reactive, especially when you look at Cupronickel which is generally what you'll find in coinage instead of pure copper. This means it doesn't break down, it doesn't rust, you can throw a bag of it in your muddy dirty store hole and it won't rust to pieces like an iron coin could.
Copper(copper mines) is commonly found across the historical basins of civilisation. Do a google search "copper mines world wide map," and you'll see a line of copper found around the mediterranean, up through the tigris/eur, across the silk road lines and all over china. So most major civilisations in history have not been far away from copper.