Gold has been the go-to (You might even say "standard") medium of exchange for most of human history. It's only recently that it was decoupled from currency, and look where that's lead us.
Off topic, but you might dig this, myrkul:
A history of the precious metals, from the earliest times to the present (1902)Del Mar spent 20 years working on this book. It originally came out 1880's. Well worth the hang time.