Norsemen first began raiding in what became Normandy in the late 8th century. Permanent Scandinavian settlement occurred before 911, when Rollo, one of the Viking leaders, and King Charles the Simple of France reached an agreement ceding the county of Rouen to Rollo. The lands around Rouen became the core of the later duchy of Normandy. Normandy may have been used as a base when Scandinavian attacks on England were renewed at the end of the 10th century, which would have worsened relations between England and Normandy. In an effort to improve matters, King Æthelred the Unready took Emma, sister of Richard II, Duke of Normandy, as his second wife in 1002.