“Mail was a treasured link between Civil War camps and battlefields and “back home.” Recognizing its importance to morale, the armies assigned personnel to collect, distribute, and deliver soldiers’ mail; wagons and tents served as traveling Post Offices.”
The complete article “Mail Service and the Civil War” which includes photographs is on the U.S. Post Office website.
Belle Plain (sometimes known as Belle Plains) is on Potomac Creek off the Potomac River in Stafford County, Virginia. The settlement served as a landing space for Civil War vessels carrying supplies, troops, and prisoners.