The citadels erected by Emperor Frederick II (1194-1250) in the kingdom of Sicily have always been a major source of interest for art historians, while the administrative apparatus, extended by Charles I of Anjou (1226-1285), has intrigued historians. The documents on these phenomena at the State Archives of Naples were lost in a fire in 1943. Accordingly, the material collected by Eduard Sthamer (d. 1938) has advanced to the status of an historical source. Two volumes of his edition appeared in 1912 and 1926. The documents for the planned 3rd volume were only rediscovered in 1993 and have now been edited by Hubert Houben. These documents are important for the history of art and architecture, for the study of medieval construction engineering, and also for the administrative and general history of southern Italy in the 13th century.