Though many historians date the practice of diplomacy to the Renaissance, Pierre Chaplais shows that medieval kings relied on a network of diplomats and special envoys to conduct international relations. War, peace, marriage agreements, ransoms, trade and many other matters all had to be negotiated. To do this a remarkably sophisticated system of diplomacy developed during the Middle Ages. Chaplais describes how diplomacy worked in practice: how ambassadors and other envoys were chosen, how and where they traveled, and how the authenticity of their messages was known in a world before passports and photographs.
English Diplomatic Practice in the Middle Ages