eli5: Why does it seem like every civilisation uses coins as currency even before there was a lot of mingling?

Question

I just saw a photo of old coins from like 1 or 2000 years ago and they are all round.
Why is it that they all use coins and not squares or something else completely?

In: Other

Answer 1

take a lump of metal and hit it with a hammer and you get a round coin shape, and it doesn’t have sharp corners that would ruin pockets or a pouch