Slavery was extremely common in Rome. Anyone with any real money at all owned at least one household slave. In certain periods, the slave population was significantly larger than the free population. Men who owned slaves routinely used them for sexual gratification, it was completely normal and accepted. As long as the man was the 'dominant' partner in the sex act, he could do anything at all he wanted with his slave. It took about 300 years for it to even become an offense for a man to murder his slave. Anything at all was acceptable.
It only gets interesting from the point of view of a game when you start looking into the types of sex and the types of prostitutes. Common prostitutes were not free women, they were mostly slaves, owned by the owner of the bordello - Like our protagonist, Marcus. These slaves served the needs of poor men who could not afford their own slave. For the price of a loaf of bread or a jug of wine they could fuck a whore. These women were used for sex literally dozens of times a day, until they eventually became 'used up' and were replaced.
But when it comes to anal sex, and especially oral sex (a strong taboo) with a slave, it was considered at least mildly deviant, and most house slaves were not expected to receive such attention because it would 'pollute' them or reduce their value in the eyes of the household. Such attentions were reserved for prostitutes outside the home.
If a slave prostitute for some reason became very skilled and somewhat famous, she could end up being freed and become a 'courtesan' on her own. This was really the only career open to such women other than marriage. In this game, if Marcus builds enough loyalty with each girl before she becomes famous, she will become an asset to his family.
