The oppressive heat, venomous serpents and boot-snatching muck that made the Great Dismal Swamp a barrier to European settlement ever since colonial times also made it a haven for thousands of people escaping slavery before the Civil War.

This fall, a permanent exhibition will open to provide some detail about those lives, part of an expanding effort by the National Park Service and other agencies to recast the experience of pre-war slaves. Scholars are using sites like the Great Dismal Swamp, straddling the line between North Carolina and Virginia, to highlight a little-known side of history, in which the freedom trail for slaves didn’t always run to the north.