The Treaty of Saint-Clair-sur-Epte was signed in 911 between the Frankish king, Charles the Simple, and the Viking leader, Rollo. This agreement marked a significant moment in history, as it allowed Rollo and his followers to settle in what is now northern France, in exchange for their loyalty to the Frankish crown and protection against other Viking raids. The treaty established the foundation for the future Duchy of Normandy, which would become a powerful region in medieval France. Rollo's acceptance of Christianity and his integration into Frankish society helped to bridge the gap between the Viking and Frankish cultures, influencing the development of both regions.