A collegium (plural collegia, “gathered together”; English “college”) was any association in ancient Rome with a legal personality. Such associations had various functions.

Collegia could function as guilds, social clubs, or burial societies; in practice, in ancient Rome, they sometimes became organized bodies of local businessmen and even criminals, who ran the mercantile/criminal activities in a given urban region, or rione.

Source: Collegium (ancient Rome) – Wikipedia