Treaty of Verdun
From the 5th century, the area formed part of the Frankish Empire and, in the feudal period, it encompassed the six countships of Boulogne, Montreuil, Ponthieu, Amiénois, Vermandois and Laonnois. In accordance with the provisions of the 843 Treaty of Verdun, the region became part of West Francia, the later Kingdom of France.