The Authie is a river in northern France whose 103-kilometre (64 mi) course crosses the departement of the Pas-de-Calais and the Somme. Its source is near the village of Coigneux. It flows through the towns of Doullens, Auxi-le-Château, Nempont-Saint-Firmin and Nampont, finally flowing out into the Channel near Berck.