The French decision to build the Maginot Line was partly the result of centuries of invasions along its border with Germany, where France had few natural barriers to prevent armies from entering its territory.

After World War I, in which France had fought a bloody, desperate struggle for survival that cost the lives of nearly 1.4 million soldiers, military leaders began to debate about how best to counter Germany in a future war that they saw as inevitable, according to the 2011 book The Maginot Line: History and Guide, by J.E. Kaufmann, H.W. Kaufmann, Aleksander Jankovic-Potocnik and Patrice Lang.

Marshal Joseph Joffre, a hero from the 1914 Battle of the Marne, argued that the best approach was to build a few heavy fortifications inside France to protect key areas against invaders, while allowing the French army room to maneuver and thwart an attack. In contrast, Marshal Henri-Philippe Petain, who had led the French to victory at the Battle of Verdun in 1916, favored a continuous line of lighter fortifications.

Ultimately, the Maginot Line’s designers mixed the two concepts together, and came up with a plan for a single continuous line, which featured imposing fortresses with other defenses between them.

French engineers also studied the ring of forts around Verdun, which had been bombarded by artillery during the 1916 battle. Though military leaders at the time had expected them to fail, the engineers discovered that the walls had held up well and that the scattered gun turrets had been effective. They developed plans for concrete and steel fortifications with plenty of firepower, and extensive underground passages.

One of the big proponents for a heavily fortified border was Andre Maginot, a French politician who had suffered such serious injuries in World War I that he needed crutches to walk. In his two stints as Minister of War during the 1920s, Maginot managed to convince the French Parliament to allocate funds for the project. Journalists started calling it the Maginot Line, in recognition of his role.

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In addition to the likelihood of a future conflict, Maginot had another very compelling argument on his side. The toll that World War I had taken upon the French population meant that the country faced a future shortage of soldiers to defend the country against Germany, which also suffered heavy losses but had almost twice the population. Heavy fortifications seemed like a good way to provide protection until manpower returned to normal.

Construction began in the late 1920s, and by 1936, the Maginot Line was largely complete. When French officials gave Winston Churchill a tour of the Maginot Line in August 1939, he was impressed by what he saw.

“The French front cannot be surprised,” the future Prime Minister wrote, according to Paul Addison’s 2007 biography Winston Churchill. “It cannot be broken at any point, except by an effort which would be enormously costly in life and take so much time that the general situation would be transformed while it was in progress.”

But despite all its steel and concrete, the Maginot Line had at least one glaring flaw: While the border with Germany was protected, the fortifications stopped at the beginning of the border with Belgium, which in the 1930s was a French ally. After Belgium declared its neutrality in 1936, French defense minister Edouard Daladier sought additional funding to extend the Maginot line along France’s border with Belgium, but those fortifications were never completed.

With the Maginot Line blocking the Germans from directly crossing the French-German border, the French military knew that the Germans would have to go through Belgium to attack. But they counted on the natural barrier of the Ardennes, a dense forested area with rough terrain and few roads, to narrow the area that the Germans could cross.

But Lt. Gen. Heinz Guderian, Germany’s top tank commander, had spent time in the Ardennes during World War I, and knew the area well enough to map out the terrain and find a way to get through, as Bevin Alexander describes in Inside the Nazi War Machine. That emboldened the German army to gamble on getting through the wilderness—and it paid off.

As French historian Michael Bourlet explained in a 2020 interview, the Germans were able to outmaneuver the French army that had been set northward to fight them. As a result, the Germans were able to encircle the French and their British allies and drive them back toward the coast, and then head south to Paris.

Once the Germans were behind the Maginot Line, they also were able to attack it from the rear and capture the fortifications, taking more than 500,000 prisoners.

Today, “Maginot Line” has become a catchphrase used to describe an inadequate barrier that provides a false sense of security.

READ MORE: Did WWI Lead to WWII?

The Maginot Line: The 'F-35' of World War II Never Stood A Chance. Nov. 9, 2019. The National Interest.
Andrew Roberts. The Storm of War: A New History of the Second World War. Publisher: Harper Collins.
Why France's World War II defense failed so miserably. Business Insider.