Arnulf I greatly expanded Flemish rule to the south. He took over all or part of Artois, Ponthieu, Amiens, and Ostrevent. Arnulf exploited the conflicts between Charles the Simple and Robert I of France, and later those between Louis IV and his barons. In his southern expansion Arnulf had conflict with the Normans. They were trying to secure their northern frontier. This led to the 942 murder of the Duke of Normandy, William Longsword, at the hands of Arnulf's men. The Vikings became less of a threat during the later years of Arnulf's life. He worked on reforming his county government.