Before revision: The French Maginot Line, constructed from 1929 to 1939, was a chain of fortresses, bunkers, retractable turrets, outposts, obstacles, and sunken artillery emplacements, all linked by an extensive shell-proof underground tunnel network.
After revision: The French Maginot Line, constructed from 1929 to 1939, was a chain of fortresses, bunkers, retractable turrets, outposts, obstacles, and sunken artillery emplacements, all linked by an extensive shell-proof tunnel network.