He was the son of Baldwin I of Flanders and Judith, a daughter of Charles the Bald and as such a descendant of Charlemagne. In 884 Baldwin married Ælfthryth (Ælfthryth, Elftrude, Elfrida), a daughter of King Alfred the Great of England. The immediate goal of this Anglo-Flemish alliance was to help Baldwin control the lower Canche River valley. The early years of Baldwin's rule were marked by a series of devastating Viking raids into Flanders where Little north of the Somme was left untouched.[4] By 883 he was forced northward to the flat marshes of the pagus flandransis which became the territory most closely associated with the counts of Flanders from that time on.[4] Baldwin constructed a series of wooden fortifications at Saint-Omer, Bruges, Ghent, and Courtrai and seized those lands abandoned by royal and ecclesiastical officials.[5] Many of these same citadels later formed castellanies housing government, militia and local courts.[4] In 888 the west Frankish king Charles the Fat was deposed and there were several candidates for his replacement.[6] As he was a grandson of Charles the Bald, Holy Roman Emperor and King of West Francia, Baldwin could have, but did not, compete for the crown of western Francia.[5] Instead Baldwin joined others in trying to convince the East Frankish king Arnulf to also take the west Frankish crown, but Arnulf declined.[6] The Robertine Odo, Count of Paris, was elected king[7] but Odo would not support Baldwin's attempts at gaining control of the abbey of St. Bertin the two fell out and while Odo attacked Baldwin at Bruges he could not prevail.[6] Baldwin continued his expansion to the south and gained control of Artois including the important abbey of St. Vaast. But when that abbey came under the jurisdiction of Archbishop Fulk of Reims Baldwin had him assassinated in 900. When his attempts to expand further into the upper Somme River valley were opposed by Herbert I, Count of Vermandois Baldwin likewise had him assassinated. He died 10 September 918[8] at Blandinberg (near Ghent) and was succeeded by his eldest son Arnulf I of Flanders. His younger son Adalulf was (the first) count of Boulogne.