But one guard can guard a lot more than $20m.  A normal-size briefcase holds about $1m in $100 bills, (<a href="http:&#x2F;&#x2F;www.cockeyed.com&#x2F;inside&#x2F;million&#x2F;million.html" rel="nofollow">http:&#x2F;&#x2F;www.cockeyed.com&#x2F;inside&#x2F;million&#x2F;million.html</a>, <a href="https:&#x2F;&#x2F;www.quora.com&#x2F;How-many-$100-bills-can-you-fit-in-one-of-those-metal-courier-suitcases" rel="nofollow">https:&#x2F;&#x2F;www.quora.com&#x2F;How-many-$100-bills-can-you-fit-in-one...</a>), or presumably about five times that if you store in 500-euro notes.  So in the end people with amounts of cash in the single- or double-digit millions would probably get together and hire one guard instead of many (you don&#x27;t get rich by spending six figures a year unnecessarily) ... and we start heading back towards reinventing banks.