The Brigade de fusiliers marins (Rear-Admiral Pierre Alexis Ronarc'h were sent from Pierrefitte, near Paris, on 7 October, to Flanders and by18 October were at Dixmude. The fusiliers marins comprised six battalions of mostly reservists, with 6,670 men of whom 1,450 were fusiliers, a machine-gun company (16 guns) and four machine-guns in each battalion. Part of northern France and the north Belgium from the Pas-de-Calais to the Scheldt estuary had been known as Flanders since the eleventh century. West of a line between Arras and Calais in the north of France, lie chalk downlands covered with soil sufficient for arable farming and east of the line, the land declines in a series of spurs into the Flanders plain. By 1914, the plain was bounded by canals linking Douai, Béthune, Saint-Omer and Calais. To the south-east, canals run between Lens, Lille, Roubaix and Courtrai, the Lys river from Courtrai to Ghent and to the north-west lies the sea. The plain is almost flat, apart from a line of low hills from Cassel, east to Mont des Cats, Mont Noir, Mont Rouge, Scherpenberg and Mount Kemmel. From Kemmel, a low ridge lies to the north-east, declining in elevation past Ypres through Wytschaete, Gheluvelt and Passchendaele, curving north then north-west to Dixmude where it merges with the plain. A coastal strip about 10 miles (16 km) wide, is near sea level and fringed by sand dunes. Inland the ground is mainly meadow, cut by canals, dykes, drainage ditches and roads built up on causeways. The Lys, Yser and the upper Scheldt have been canalised and between them the water level underground is close to the surface, rises further in the autumn and fills any dip, the sides of which then collapse. The ground surface quickly turns to a consistency of cream cheese and on the coast troop movements were confined to roads, except during frosts.
The rest of the Flanders Plain is woods and small fields, divided by hedgerows planted with trees and cultivated from small villages and farms. The terrain was difficult for infantry operations because of the lack of observation, impossible for mounted action because of the many obstructions and difficult for artillery because of the limited view. South of La Bassée Canal around Lens and Béthune was a coal-mining district full of slag heaps, pit heads (fosses) and miners' houses (corons). North of the canal, the cities of Lille, Tourcoing and Roubaix form a manufacturing complex, with outlying industries at Armentières, Comines, Halluin and Menin, along the Lys river, with isolated sugar beet and alcohol refineries and a steel works near Aire. Intervening areas are agricultural, with wide roads on shallow foundations, unpaved mud tracks in France and narrow pavé roads along the frontier and in Belgium. In France, the roads were closed by the local authorities during thaws to preserve the surface and marked by Barrières fermėes, which in 1914 were ignored by British lorry drivers. The difficulty of movement after the end of summer absorbed much of the civilian labour available on road maintenance, leaving field defences to be built by front-line soldiers.