sburg, on the western side of Antietam Creek, a sluggish stream with few fords, spanned by four stone bridges.
On the right of the National line were the corps of Hooker and Sumner.
In the advance, and near the Antietam, General Richardson's division of Sumner's corps was posted.
On a line with this was Sykes's (regular) division of Porter's corps.
Farther down the stream was Burnside's corps.
In front of Sumner and Hooker were batteries of 24-pounder Parrott guns.
Franklin's corps and Couch's division were farther down the valley, and the divisions of Morrell and Humphrey, of Porter's corps, were approaching from Frederick.
A detachment of the signal corps, under Major Myer, was on a spur of South Mountain.
As McClellan prudently hesitated to attack, the Confederates put him on the defensive by opening an artillery fire upon the Nationals at dawn （Sept. 16, 1862). He was ready for response in the course of the afternoon, when Hooker crossed the Antietam with a part of his c