National redoubt

A national redoubt or national fortress is an area to which the (remnant) forces of a nation can be withdrawn if the main battle has been lost or even earlier if defeat is considered inevitable. Typically, a region is chosen with a geography favouring defence, such as a mountainous area or a peninsula, to function as a final holdout to preserve national independence and host an effective resistance movement for the duration of the conflict.

From the middle of the 19th century until 1914 the fortress city of Antwerp was the official National Redoubt of Antwerp in Belgium.

Fortress Antwerp was a defensive belt of fortifications built in two rings to defend Antwerp. Antwerp was designated to be a national reduit (Réduit national (French) or De versterkte stelling Antwerpen (Dutch)) in case Belgium was attacked. It was built in the period 1859–1914. In total it encompasses a belt of fortifications of 95 km.

In 1940 Brittany was briefly considered as such in the last stages of the Fall of France, but proved impractical.

Until 1920, the "Fortress Amsterdam" was the national redoubt of the Netherlands. Between 1920 and 1940, Fortress Amsterdam was extended to Fortress Holland, to include a larger part of the country's heartland. In both cases, neither "redoubt" proved defensible even though the Dutch Water Line, a precursor in the Netherlands managed to stop the advances of the French troops in the Rampjaar 1672, providing the Dutch with the needed time to gain the upper hand.

Since the early 19th century to the World War II, Lisbon was considered the national redoubt of Portugal. Besides being the capital, the largest city and the major port of the country, Lisbon was considered the last defensible redoubt in case of an invasion of Portugal by a major power. During this period, successive systems of defense were implemented.

The first major defense system of Lisbon was built during the Peninsular War, as the Lines of Torres Vedras. These consisted in two lines of fortifications that protected the region of Lisbon (with a third line around the coastal fortress of São Julião da Barra). The Lines of Torres Vedras were able to block Masséna's 1810 offensive.

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