One of the greatest geographical treatises of the Middle Ages was written by the Moroccan Muhammad al-Idrisi for Roger, and entitled Kitab Rudjdjar ("The book of Roger"). The Norman Kingdom of Sicily under Roger II was characterised by its multi-ethnic nature and religious tolerance. Normans, Jews, Muslim Arabs, Byzantine Greeks, Longobards and "native" Sicilians lived in harmony. He dreamed of establishing an Empire that would have encompassed Fatimid Egypt and the Crusader states in the Levant. Islamic authors would marvel at the tolerance of the Norman kings: