Wikipedia:

Union soldiers entrenched along the west bank of the Rappahannock River at Fredericksburg in the Battle of Chancellorsville.

This is a photograph misidentified by the National Archives as a Mathew Brady work, allegedly a view of Union soldiers in the trenches around Petersburg, Virginia, in 1865. According to Frassanito, William A.,Grant and Lee: The Virginia Campaigns 1864–1865, Scribners, 1983, ISBN 0-684-17873-7, pp. 422-23, “One of the most famous of all photographs traditionally captioned as a Brady view — showing Union soldiers in the trenches before Petersburg — is in reality an A. J. Russell photograph depicting Union soldiers of General William T.H. Brooks’s division, Sedgwick’s corps, entrenched along the west bank of the Rappahannock River at Fredericksburg, just prior to the battle of May 3, 1863.