In the north of the department; the Oise, traversing the northwest, with its tributaries the Serre and the Aisne, the latter of which joins it beyond the limits of the department; and the Marne and the Ourcq in the south.
In July 1780 Gallatin and his friend Henri Serre (d.
De la Serre) as "one of the finest, largest and best-situated cities not only of Brabant but of the whole of Europe.
De la Serre declared that if he had seen there an apple tree he would assuredly have taken it for an earthly Paradise."
Sa langue est excellente; son style Clair, serre, simple, d'ordinaire assez monotone, vous plait par sa saveur archaique et quelquefois par une certaine grace et une certaine malice."
Flowing through the district of Thierache, it divides below Guise into several arms and proceeds to the confluence of the Serre, near La Fere (Aisne).