Fortified region of Belfort

Located in northeastern France between Épinal and Besançon, the primary line was built in the late 19th century to deal with advances in artillery that had made older defensive systems obsolete.

[1] Shortly after the French defeat in the Franco-Prussian War of 1870–1871, Belfort, an important road and railway node and the frontier cities of Épinal, Toul and Verdun were chosen to constitute the first line of defense against an invasion from the annexed French provinces of Alsace and Lorraine.

The fortifications were part of an extensive network of new forts proposed and carried out by Raymond Adolphe Séré de Rivières.

The fortifications of the Séré de Rivières system of the 1880s were designed to defend the new eastern frontier following the Franco-Prussian War.

With the recovery of these territories following World War I, most of the Séré de Rivières forts were deep in the interior of north-eastern France and not useful.

[2] A new région fortifiée de Belfort (RFB) was again proposed in 1922 by the Territorial Defense Commission (commission de défense du territoire), which identified three potential invasion routes from Germany, the Belfort Gap, between the Vosges Mountains and the Rhine and across the Lorraine plateau The committee's final report proposed a continuous fortification from the Swiss border north to the Lauter and west to Longwy, with the area of the Sarre, which faced the demilitarized area of the Saarland, left unfortified.

The report recommended the creation of a line of defenses about 25 km (16 mi) to the east of Belfort, with heavier fortifications to the north and lighter positions to the south.

[5][6] The two Perches forts of the original belt were retained and rebuilt by Séré de Rivières, by reason of their strategic value during the final stage of the Siege of Belfort in 1870–71.