On 27 January 1186 the German king Henry VI, son and heir of the Roman Emperor Frederick I ‘Barbarossa’, married Constance of Hauteville, heir to the throne of Sicily, in the Basilica of St Ambrose in Milan. The royal wedding sealed the union of the Kingdom of Sicily and the Holy Roman Empire, creating an enormous empire stretching from the shores of the North Sea to the beaches of Africa. The union also incited a major geopolitical conflict dominating European politics in the thirteenth ...