Baldwin was given rule over Flanders with the title of (count of a ) of Flanders. He protected Flanders for the next fifteen years from Vikings. He became known for his harsh treatment of anyone attacking Flanders. This later gave him the name "Baldwin Iron Arm". In 867 Baldwin built a castle at Ghent to protect from Viking raids. The city built up around the castle. Ghent became the seat of his . Baldwin also built a castle at Bruges, the port city on the North Sea. It too was for the purpose of stopping Viking . When Charles the Bald died in 877, Baldwin faithfully supported his son, Louis the Stammerer, helping him become king of the Franks. Baldwin died in 879.