Former Slaves Serve as Union Soldiers

In this photograph (by William R. Pywell) African-American men (serving as Union soldiers) stand in front of a former "slave pen" in Alexandria, Virginia. 

The Library of Congress provides more background about the picture:

"Not until after the Emancipation Proclamation was in force as of January 1, 1863, did Union officers actively recruit African American soldiers, although some black men were unofficially part of segregated units in a few states. By the end of the Civil War, one out of every eight Union soldiers was a black man. This image is symbolic because the soldiers stand in front of a location where black slaves were held for auction, stripped, examined, and bought and sold before interested purchasers."

Credits

William R. Pywell.
Slave Pen in Alexandria, Va.
1862
Copyprint.
Image, Library of Congress.