The Collegium which Vorenus controls was one of the most powerful crime organizations in Ancient Rome. The gang controlled the busiest river docks on the Tiber River, where most of the grain shipments were unloaded. This put the primary food supply for Ancient Rome in the hands of criminals.
Since Ancient Rome had no official police force, politicians were forced to work directly with crime bosses to assure peace in the streets.
In the scene where Pullo is hiring new people for their crime gang a standard can be seen that bears L. Vorenus' name and has a three headed dog on it as well. The three headed dog is Cerberus, guardian of the underworld which fits with Lucius claiming to be a son of Hades