...troops, to reinforce the right. Six battalions of Sykes's regulars had been thrown across the Antietam bridge on the main road, to attack and drive back the enemy's sharpshooters, who were annoying Pleasonton 's horse-batteries in advance of the bridge. Warren's brigade, of Porter's corps, was detached to hold a position on Burnside's right and rear; so that Porter was left at one time with only a portio...