Currency was traditionally made of precious metals which often gave them a rather high starting point of value. It also made them inflation resistant meaning the real value only grew over time. For instance in the Roman Empire an aureus [1] was worth 25 denarii (prior to inflation) and was about 2cm in size, so roughly the same size as a dime, made of pure gold. And a denarius was worth about a day's wages. So you could comfortably hold decades of wages in a small coin purse. And as inflation ravaged the Empire a single aureus gradually came to be worth thousands of denarii.

[1] - https://en.wikipedia.org/wiki/Aureus