[Illustration: BATTLE OF FAIR OAKS. =UNION TROOPS.= 1 Casey's division. 2 Couch's " 3 Heintzelman's corps. 4 Sumner's " =REBEL TROOPS.= 5 Whiting. 6 Longstreet. 7 Anderson. 8 Fair Oaks. 9 Seven Pines.][23] [Footnote 23: The diagram represents the position of the troops at the beginning of the battle.] Casey's division faced towards Richmond; Naglee's brigade was on the railroad,--two regiments north of it; Wessell's brigade was in the center, near "Fair Oaks," and Palmer's was on the left, south of the Williamsburg road. Spratt's battery was near the Oaks. Regan's battery was in rear of Spratt's. Bates's battery was south of the Williamsburg road, in a redoubt, while Fitch's battery was in rear of the redoubt. Couch's division at Seven Pines was lying with Graham's brigade between the Williamsburg road and the railroad, Devens's brigade on the Williamsburg road, and Peck's brigade on the left. Up to twelve o'clock there was little firing except by the pickets, and the men in Casey's command laid aside their arms and prepared to eat dinner. Soon after noon two shells were thrown into Casey's camp. Suddenly there was a heavy roll of musketry in the woods. Officers sprang to their feet. They knew that it portended trouble. There was a quick saddling of horses and buckling on of belts. Orders were issued in imperious tones. The men left their coffee-pots and plates of rice, seized their guns, and formed in line. Casey's division was composed of undisciplined troops which had joined the army after its arrival upon the Peninsula. The men had had no experience, and yet they were placed in advance, nearest the enemy,--an oversight which was dearly paid for. The force which Johnston had brought out numbered not far from thirty thousand. Casey's division numbered not far from seven thousand. Like an avalanche was the advance of the Rebels upon this small, undisciplined force. Generals Anderson, D. H. Hill, Jenkins, Pegram, and Wilcox swept along the Williamsburg road, striking Palmer's brigade on the left flank.