5. A Roman (Or Byzantine) Rivalry
Two major factions of chariot racing hooligans had developed by the 6th century A.D.: the blues and greens. Much like the Yankees and Red Sox rivalry in baseball, these two factions vehemently opposed each other with feuds often spilling over into violence. However, harsh actions against both gangs by the Emperor Justinian led to a brief truce that united the blues and greens against the empire.
