The marker for the Cavalry Division of the Army of the Potomac is on the west side of Boonsboro Pike, west of Rodman Avenue. (Boonesboro Pike tour map)

From the marker:

U.S.A.

Cavalry Division

Brig. Gen. Alfred Pleasonton, Commanding.

(September 17, 1862.)

The Cavalry Division was stationed along the west bank of the Antietam Creek during the battle of September 17, in support of Horse Batteries A, B and L (Consolidated), and M, of the Second U. S. Artillery, and Batteries C and G (Consolidated) of the Third Artillery, which were established on the crest of the ridge in front of this point. This Division occupied a portion of the ground between the left flank of the Second and right flank of the Ninth Army Corps, and covered the approaches to the bridge across Antietam Creek. At night the Division was withdrawn.

No. 21.