The Norman kingdom of Italy created in 1130 for Roger II comprised the lands he had inherited in Calabria and Sicily from his father, Count Roger I, the mainland territories ruled by his cousin, Duke William of Apulia, until his death in 1127, and the lands of those great men of southern Italy who were or became Roger's vassals. These lands had never previously been united under a political authority of their own, and had not shared a common history since Justinian's reconquest of Italy six hundred years before. The establishment of the kingdom was made possible by the diffusion of Norman lordships throughout most of these lands in the hundred years before 1130, though it is misleading to regard Norman successes in those years as stages in a long-term plan to unite them eventually into a single Norman state. Norman military commanders had taken over the governments of the regions they controlled at various times, and not all these political authorities actually still survived in 1130. The units of the kingdom were as disparate as can be imagined. Apart from the leaders and their vassals, often also of Norman descent, the units had very little in common. The larger they were, the more complex their structures. Roger II's own lands combined Calabria, conquered from the Greeks, and Sicily, taken from the Muslims.