The siege of Saint-Denis by the Russian army in 1814 underscored the site's strategic value.
Thus, during the reign of Louis-Philippe-within the framework of the construction of the Parisian fortification system-three forts were built in order to protect the secter bounded by the canal, the Seine and the Paris rampart. To the north, the Double Couronne fort commanded the arrival of three major roads from Le Havre, Calais and Gonesse. Dykes linked this fort to the Est and La Briche forts, blocking the Rouillon and offering the possibility of using the Seine to flood the marshy zone. In 1870, 25,000 members of the National Guard and 274 cannons were deployed to occupy this structure. Saint-Denis held out against the Prussian siege for more than four months.
The interest that the military engineers took in the configuration of the land bordering these fortifications has left us with a set of maps in which the relief is indicated by contour lines. Given the scope of the earthworks which turned off these zones at the time of urbanization, such documentation is extremely precious for understanding the original state of the surrounding countryside.
Map of the floods of 1869-1870.
© Service historique de l'armée de terre / Archives départementales de la Seine-Saint-Denis.