Vermandois was a French county during the Merovingian period. In the tenth century, it was organized around two castellan domains: St Quentin (Aisne) and Péronne (Somme). Pepin I of Vermandois, the earliest of its hereditary counts, was descended in direct male line from the emperor Charlemagne. More famous was his grandson Herbert II (902–943), a man absolutely devoid of scruples, who considerably increased the territorial power of the house of Vermandois, and kept the lawful king of France, the unlucky Charles the Simple, prisoner for six years. Herbert II was son of Herbert I, lord of Péronne and Saint Quentin, who was killed in 902 by an assassin in the pay of Baldwin II, Count of Flanders. His successors, Albert I, Herbert III, Albert II, Otto and Herbert IV, were not as historically significant.