Cathy the connection to the dark ages and the black plague is a mythos spread by the mafia themselves. They like to see their roots in the 1298 uprising against the Anjou, "Vespera Siciliana" (the black plague, came also around than 1346 over Messina into Europe/Sicilia), and a legendary secret society of that time the "beati paoli". Historicans (Lupo...etc, nonitalian Dickie) proofed that this a legend. Beside other groups, the Cosa Nostra mainly originated from the gabelloti, criminals, who controlled the land for the lords, and defended it against the poor workers/farmers.