The National Mall in Washington DC is one of America’s most important public spaces. And space is the key, writes Christopher Knight. But Congress seems intent on cluttering it up with ever more memorials and tributes, which will certainly ruin a grand place. “Approved or proposed Mall additions now include memorials to President Reagan, Martin Luther King Jr., terrorist victims, Native Americans and soldiers lost in peacekeeping missions. Then there’s the network of tunnels, underground security checkpoints and surveillance cameras newly suggested for the Washington Monument. Like other burgeoning examples of a post-Sept. 11 ‘architecture of fear,’ these schemes would destroy the monument in order to save it.”