English: The steam engine "Firefly" on a trestle of the Orange and Alexandria Railroad. This view by Russell documents stability testing of a new wooden trestle bridge built quickly by the United States Military Railroad engineers to replace a masonry bridge destroyed by the Confederates. Atop the box car trailing the engine is a pair of armed sentries; others are on the rail tracks and bridge foundation. The top-hatted figure in the foreground is unidentified, but he may be the photographer himself or a civilian railroad engineer working for General Herman Haupt, commander of the United States Military Railroad.