Public domain
Petersburg, Virginia. Earthworks in front of Petersburg. (The 27 foot ditch at Fort Gilmer, Guard against Federal mines)
From the collection of Library of Congress. Free to download, adapt and use — no permission needed.
Credit linePetersburg, Virginia. Earthworks in front of Petersburg. (The 27 foot ditch at Fort Gilmer, Guard against Federal mines). 1865. Civil War Glass Negatives, Library of Congress. Public domain.