The treaty of Saint-Clair-sur-Epte (911) is the foundational document of the Duchy of Normandy, establishing Rollo, a Norse warlord and Viking leader, as the first Duke of Normandy in exchange for his loyalty to Charles III, the king of West Francia, following the Siege of Chartres. This treaty included a land grant of farmable coastal land from Charles the Simple to Rollo in return for his fealty and protection against other Viking groups that had been regularly bombarding the northern coastline.[1] This treaty effectively changed how mainland Europe knew to resolve ongoing bombardments from the Vikings.[2]
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was invoked but never defined (see the help page).