The War Department marker for Seymour’s Bivouac is on Mansfield Avenue at Smoketown Road, near the monument to the 12th Pennsylvania Cavalry. (Smoketown Road North tour map)

The marker shows the position where Seymour’s Brigade of Meade’s Pennsylvania Reserves spent the night before launching the opening attack of the Battle of Antietam the next morning. As they moved across Antietam Creek and into position on the north end of the battlefield they ran into Confederate pickets, prompting a brisk firefight that ended as darkness fell and the Confederates pulled back to their main lines. The movement and the fighting gave away McClellan’s intentions to attack at this point in the morning.

U.S.A.
First Army Corps
Seymour’s Briade of Meade’s Division, after its engagement with the enemy of September 16, 1862, bivouacked on either side of the road at this point , with pickets thrown forward in the east woods.