Patronage, or the patron-client system, has been described as the glue that held the fabric of the Roman Empire together. It is because the barbarian invasions broke these ties of intricately connected networks that the Empire collapsed (or so they say), and feudalism was the result—the child of patronage but far less interconnected.

Practically everyone in the Roman world was a client of somebody (probably several somebodies) and a patron of somebody else (again, generally more than one person). The emperor was client to no one, and the poorest townsfolk, and slaves, had no clients of their own, but between these two extremes stretched an intricate network based on mutual obligation and unequal status.

First, a clarification: "Free laborer" is almost an oxymoron in Roman society. Free men who worked would likely be shop owners but never shop workers—the workers were slaves. Hence even the poorest of free men were people of some means—thus their position in the patronage system.

Every morning at sunrise, it was the obligation of a client to pay a brief visit to the house of his patron(s), doing small-scale homage (called salutatio). Lined up in their ceremonial togas (not an inexpensive article of clothing), the various clients would be admitted, in order of status, into the patron's antechamber where they would receive a symbolic gift of money (a sportula), enough to buy food for the day (this might vary depending on the status and wealth of the patron in question).

Patrons were protectors, benefactors, mentors, and power-jockeys, in the sense that they often wrote letters to recommend young clients for public office. Patrons might represent their clients in court, give gifts of food and money, protect the powerless from the abuses of the powerful, and so on. The main thing patrons received in return was honor. Clients identified themselves by their patrons' names, spreading the reputation of their generous and beneficent patrons far and wide. Benefactors expected to receive copious recognition for their gifts, including public inscriptions, places of honor at banquets, and the like. In addition, patrons could require services of their clients, in return for some particularly generous gift. As a simple example, a patron paying for a banquet for a collegium (a fraternity of craftsmen or devotees of the same god) would have the privelege of setting the menu for the banquet.

Freed slaves, too, automatically became clients of their former masters, a form of clientage that sometimes almost amounted to a renewed slavery. Interestingly, there was a good deal of competition and jealousy between freedmen clients and other clients—because the freedmen tended to be more wealthy than the others! This competition not infrequently erupted into brawls during banquets, it seems.

The obvious question, then, is what all this has to do with the game. Well, largely that's up to the individual DMs and players. Characters may exist to an extent outside the system—especially escaped slaves and other criminals. However, there are (I think) interesting and exciting possibilities regarding how this system could function in the campaign. At a basic level, a mage PC's mentor could be that character's patron, and be a source for, among other things, spells, food, lodging, letters of recommendation when traveling, and so on. There's an enormous potential for intrigue as client PCs get caught up in the personal and political affairs of their patrons, with the advantage (over previous adventures involving political intrigue) that the NPCs involved will be well known to the characters. The patron-client system can provide a place for PCs in the very well-ordered society of the Roman world (it is lawful, after all), which may simply amount to a foothold from which to fight against that structure. In any event, it can give characters more depth and a more interesting background from which adventures can be drawn.