Institutionally, the Normans combined the administrative machinery of the Byzantines, Arabs, and Lombards with their own conceptions of feudal law and order to forge a unique government. Under this state, there was great religious freedom, and alongside the Norman nobles existed a meritocratic bureaucracy of Jews, Muslims and Christians, both Catholic and Eastern Orthodox. The Kingdom of Sicily thus became characterized by Norman, Byzantine Greek, Arab, Lombard and "native" Sicilian populations living in harmony, and its Norman rulers fostered plans of establishing an Empire that would have encompassed Fatimid Egypt as well as the Crusader states in the Levant. One of the great geographical treatises of the Middle Ages, the "Tabula Rogeriana", was written by the Andalusian al-Idrisi for king Roger II of Sicily, and entitled "Kitab Rudjdjar" ("The Book of Roger").