This is simply fascinating (and maybe NSFW):

[These coins] were used in ancient Rome to request and pay for different “services” in brothels and from prostitutes on the street. Since there were a lot of foreigners coming to the city that did not speak the language and most of the prostitutes were slaves captured from other places the coins made the transactions easy and efficient. One side of these coins showed what the buyer wanted and the other showed the amount of money to be paid for the act.
The value of a handjob, the value of a blowjob, the value of some gay sex, the need to communicate desire, the roads leading to Rome, the slave economy.


Thanks for the link goes to one, Christopher Ryan, of the two authors of Sex at Dawn.