Hamas’s easy defeat of Israel’s so-called Iron Wall with Gaza—twin lines of six metre high barbed wire fences, made from a 140,000 tons of iron and steel , backed up with an underground concrete skirt to block tunnels, and a dense array of radar, thermal cameras, movement sensors and remotely-operated machine-guns—has set military planners across the world wondering if modern static defences are again as useless as the Great Walls which guarded medieval empires. The men of the 29 Corps, historian Jiashun Du has recorded, slaughtered the Imperial Japanese soldiers in their beds, destroyed artillery guns with grenades, and set…