Communication in the Middle Ages was better developed than often assumed and institutions, ideas, and military technology was exchanged rapidly, meaning it was possible to coordinate great military expeditions across the geographical periphery of Western Europe. Both Denmark and Portugal were closely connected to the sea and developed strong fleets, at the entrance to the Baltic and in the Mediterranean Seas respectively. They also both had religious borders, to the pagan Wends and to the Muslims, that were pushed forward in almost continuous crusades throughout the centuries. Crusading at the Edges of Europe follows the major campaigns of the kings and crusaders in Denmark and Portugal and compares war-technology and crusading ideology, highlighting how the countries learned from each other and became organised for war.