It would be natural to assume that changes and developments in the architecture of castles in the Crusader east would be reflected in western Europe, whence most of the Crusaders had come and whither at least some of them returned. In fact the evidence for this is at best ambiguous. The first problem is that castle building in western Europe varied widely: the tradition of castle buildings in the German Empire, for example, remained radically different from that in northern France. When Frederick II embarked on an impressive display of castle building in southern Italy in the first half of the thirteenth century, he made almost no use of the round towers which were universally adopted in Capetian France and Britain at the same time. Instead, at Bari, Trani, Melfi, Gioia del Colle he used high square or rectangular ones, and octagonal at the elegant and ornamental Castel del Monte, though curiously his two surviving castles in Sicily at Catania and Syracuse have round towers. It is in France north of the Loire, and by extension in England, that we should look most profitably for comparisons with Crusader work. This may be partly because, from the mid-twelfth century onwards, the vast majority of the Crusaders came from these areas. A more important reason was that, between c.1180 and c.1220, these areas were the theatre for a prolonged conflict between two powerful and developed states, the Angevin Empire and Capetian France.