Arnold & Porter senior counsel Robert Rosenbaum pulls a bundle of rolled-up maps out of a cardboard cylinder stowed in his Washington, D.C., office.

He spreads the maps across his desk. They diagram the Battle of the Wilderness, where, in May 1864, more than 160,000 Union and Confederate troops descended on a patch of forested land west of Fredericksburg, Virginia. The Wilderness marked the first time Robert E. Lee and Ulysses S. Grant led troops in battle against one another. Fighting was so fierce that brush on the forest floor caught fire, burning some wounded men alive. Nearly 30,000 men were killed or wounded.