I have searched for (and found) a number of threads talking about organized crime in ancient Rome (Crassus' extortion scheme, bandit groups, pirates). I, however, am interested in learning whether there were mafiaesque crime syndicates. As for my definition of such groups, I quote from Wikipedia:

European sociologists (e.g. Diego Gambetta) define the mafia as a type of organized crime group that specializes in the supply of extra-legal protection and quasi law enforcement.

So I am not talking about any form of organized crime, but rather a syndicate that establishes a monopoly on violence (à la Hobbes) parallel to the one of the state.

I am aware that I haven't specified an era and that the question thus covers a lot of time, but I am interested in any and all of these organized crime groups, be they from the time of the republic or from any of the various forms of the Roman empire.

Thanks a whole lot in advance!