The Italian Fascist government initiated a cultural campaign which claimed that Medieval Malta was a terra irridenta belonging by ancient right to Italy; its chief historical weapon was the Regia Deputazione di Storia di Malta. There are references to Malta and Gozo in a number of Latin, Greek, Arabic and Hebrew writings, but most of these are extremely brief and general, or they deal with particular incidents. It collected scattered references, listed sources and published documents, particularly from Naples and from Malta itself. Malta and Gozo formed part of the Kingdom of Sicily, and materials concerning them are to be found throughout the whole body of Sicilian documentation. The introduction of the compass in the thirteenth century may have opened up Malta to shipping in an altogether new way. Byzantine Malta was a place of exile, and possibly a minor naval base; it was strong enough to hold out against the Muslims until 870.