After World War I, the French were understandably worried about another invasion. They had suffered many losses in the first world war and wanted to prevent future defeat from their rivals. The general consensus in France was to build a defensive wall – and thus the Maginot Line was built, named after French minister of defense AndrĂ© Maginot. It was a series of fortifications along the French borders with Germany and Italy; its chief design was in preventing future invasions.

The line itself was a pinnacle of modern defenses. Instead of a single wall, it was a series of over five hundred buildings – some key forts, others small bunkers, all designed to slow the advance of an enemy. The bunkers themselves were large – some over six stories deep – and had all living necessities, plus hospitals and trains to get from bunker to bunker. This is to say nothing of the impressive armaments put on the line. If the next great war were to become dependent on the trenches, as in World War I, then the French would be ready.

Yet on May 10, 1940, Germany invaded France. Within two months France surrendered. What had gone wrong?

France’s first mistake was depending too much on the Maginot Line without mobile forces. There were two main thoughts on the future defense of France: many had learned their lesson from the first war, with its endless trench battles. If France were to fall in another trench war, they would be much better defended with stronger fortifications on their side. However, a few men, such as Charles de Gaulle, argued that more mobile units were needed, such as tanks and aircraft. Their protests went unheeded. This lack of a strong mobile force caused France to become stymied in the face of a German blitzkrieg.

The second, and much more damaging problem, was France’s disregard of defense around the Ardennes Forest and Belgium. It was believed by the French that tanks could not navigate the forest, so it was left out of the Maginot Line. Belgium and France were in an alliance at the time of the Maginot Line’s conception, so it was left largely undefended as well. Unfortunately for France, German forces cut through the country from Belgium, the Netherlands, and most damningly the Ardennes Forest. Germany managed to get to the core of France without ever having to deal with the Maginot Line.

Many cite the Maginot Line as the ultimate act of hubris – that simply building a wall is not enough to defend oneself against an obvious threat such as Germany. However, in its defense, it did serve its main purpose – to slow down the attacking force. It successfully repelled the Italians until Germany came, and even then the Maginot Line never actually fell to Germany – it was simply bypassed, and eventually had to surrender with the rest of France.