Just some alternative math...

In 1964, the minimum wage in the U.S. was $1.25 (quarters were 90% silver then so you are talking about 5 silver quarters). Each quarter had approximately 5.62499846 grams of pure silver (that changed in 1965) so that equates to 28.1249923 grams of silver per hour. This works out very roughly to $15/hr at the current price of silver. The Federal minimum wage is currently only half that. Of course, this is only going back a relatively short time compared to the Roman Empire. Interestingly, a lot of people support a $15 minimum wage.