The great port of Le Havre stands at the mouth of the Seine estuary, which opens into the bay of,the Seine on the east.
The Seine descends from the Langres plateau, flows northwest down to Mry, turns to the west, resumes its north-westerly direction at Montereau, passes through Paris and Rouen and discharges itself into the Channel between Le Havre and Honfleur.
The longest established is that of Normandy, having its centres at Rouen, Havre, Evreux, Falaise and Flers.
Its chief lines ran from Paris:to Le Havre via Mantes and Rouen, to Dieppe via Rouen, to Cherbourg, to Granyule and to Brest.
Of the coast defences the principal are Toulon, Antibes, Rochefort, Lorient, Brest, Olron, La Rochelle, BelleIsle, Cherbourg,St-Malo, Havre, Calais, Gravelines and Dunkirk A number of the older fortresses, dating for the most part from Louis XIV.s time, are still in existence, but are no longer of military importance.