Mutzig, France – First stop on my annual visit to France's mighty Maginot Line forts is this lovely Alsatian town. Mutzig was built by the Germans 1893-1916 to defend against enemy approaches to the important city of Strasbourg. It was – and remains – the largest modern fortress in Europe.

The vast fortress, which covers over 800 acres, was never attacked during World War I by the Germans or French. But as Europe's first important fortress made of concrete and fully electrified, it was eagerly studied by French engineers and served as a template for the Maginot Line forts two decades later.

Both world wars showed the vulnerability of fixed fortifications. An enemy will always find a way round them or discover a fatal weakness. In regard to the 200-mile-long Maginot Line, the forts did not fail. They held out to the bitter end. The reason for France's stunning defeat in 1940 was the failure of its field army and its blockheaded generals. Interestingly, a French parliamentary deputy with the effervescent name of Perrier precisely predicted where the Germans would break through the Ardennes Forest in 1940.