Flag of Truce Civil War Cover

My favorite Civil War covers!

...Because they have Confederate AND Union stamps.  Quite rare.  Most are from captured Confederates held in Northern prison camps. Each cover is hand-stamped “Prisoner Letter Examined,” shows the prison name, and most have handwritten “Flag of Truce.”  Postmarked in the Union and again when it entered the Confederate system in Richmond.  Condition fine, considering they are over 150 years old and were in the Civil War.   Covers vary.