Continuing on the discussion of Norman politics, the establishment of an established set of Norman laws was also majorly influenced by the local populations living on the southern Italian Peninsula prior to Norman rule. Before the legal reformations of Roger II of Sicily, there was a lot of legal disconnection between the many factions and cultures among the southern Italian powers. This highlights both the ineffectiveness and lack of consolidation of Norman legal administration within their own realm. This meant that in order for the Normans to effectively maintain peace and law in their own realm, they had to rely on the many local customs and administrations that laid out temporary legal works. As more land and cultures began to be incorporated into the Norman realm, the legislative and bureaucratic landscape of Norman society also incorporated these pre-existing customs and administrations, both building upon them and eventually evolving these methods into their own Norman code of law.

Two key figures in Norman legal reform are Roger I and Roger II. Both served as the Counts of Sicily while Roger II became the first King of Sicily in 1130 CE. As previously established, Roger I pursued policies of religious and cultural tolerance within his realm. His efforts laid the groundwork for his son, Roger II, to take over. Continuing with these aspirations, Roger II encouraged peace and power in order to continue expanding and maintaining a diverse and stable Norman kingdom and its codified laws. These aspirations allowed the influences of French, Lombard, Norman, Byzantine (also referred to as Justinian), and Islamic law. The intricacy of these ideas and practices eventually accumulated into an official code of law throughout the Kingdom of Sicily, where Roger II implemented a new law code that he championed as the Assizes of Ariano.