Elaborate defensive barrier in northeastern France built in the 1930s. Named after its principal creator, Andre Maginot, it was an ultramodern defensive fortification along the French-German frontier. Made of thick concrete and supplied with heavy guns, it had living quarters, supply storehouses, and underground rail lines. However, it ended at the French-Belgian frontier, which German forces crossed in May 1940. They invaded Belgium (May 10), crossed the Somme River, struck at the northern end of the line (May 12), and continued around to its rear, making it useless.