The correct answer is ...
The tenth century.
Rollo was a Viking leader who came into France around the year 911 and settled along the Seine to besiege Paris. Though King Charles the Simple was able to hold him off for a while, eventually he negotiated a treaty which gave Rollo part of Nuestria in return for his agreement that he and his followers would stop pillaging the countryside. The territory Rollo acquired became the province of Normandy.
