For 3 days successful July, 1863, 2 large armies collided connected the fields astatine Gettysburg. It remains the bloodiest conflict successful U.S. history. And improbably, 155 years later, determination are inactive surviving witnesses to that infinitesimal successful time: The trees. Across 6,000 acres of Gettysburg National Military Park, rangers person documented astatine slightest a twelve "witness trees" that were live during the conflict – immoderate scarred by bullets and cannonballs – that uniquely bring America's bloody past into the present. Mark Strassmann reports.