The marker for the Fourth United States Infantry Regiment on the south side of Boonsboro Pike, just west of the Middle Bridge in front of the Newcomer barn. (Boonsboro Pike tour map)

From the marker:

U.S.A.

At 10 A.M., September 16, 1862, four Companies of the Fourth United States Infantry crossed the Stone Bridge over the Antietam at this point and took position behind the rock ledge and barn on the left of the road and under the bank on the right. At noon two companies were thrown out as skirmishers and advanced on either side of the road to the high ground about 350 yards west, to hold in check the advance of the enemy. At sunset the Fourth was relieved by the First Battalion, Twelfth Infantry. At noon of the 17th several Battalions of Regular Infantry, Pleasanton’s Cavalry Division and Horse Batteries crossed the Bridge and moved in the direction of Sharpsburg, the Twelfth Infantry acting as a support to the Artillery and advancing with it.

No. 87.