The Army of the Potomac's Third Corps under Major General Daniel Edgar Sickles began arriving on the battlefield after 5pm on Wednesday, July 1, 1863, marching over roads "rendered almost impassible by mud and the passage over it of the First and Eleventh Corps through the rain.". The last of Sickles' men would join their comrades at about 7am the next day. The men of the 3rd Corps would go into position on the left of the Union line, helping to secure the growing line of Union defenses striving to hold their ground against the Confederate attack they knew would come. The Union army's commander, Major General George Gordon Meade, would discuss the famous fishhook formation along with the portion of that ground he would order Major General Sickles' 3rd Corps to defend. "The Cemetery Ridge extended in a westerly and southerly direction, gradually diminishing in elevation until it came to a very prominent ridge called Round Top, running east and west. The Second and Third Corps were directed to occupy the continuation of the Cemetery Ridge on the left of the Eleventh Corps. The Fifth Corps, pending the arrival of the Sixth, was held in reserve." Sickles, a political General, and Meade, an army veteran, did not necessarily hold each other in the highest esteem.

As General Sickles positioned his men on July 2nd, a problem arose. Along with General Sickles, Chief of Artillery Brigadier General Henry Hunt noted a specific concern with the ground assigned to General Sickles' Corps. General Hunt would say, "The broken character of the ground in front of the southern half of our line was unfavorable to the use of artillery...The Second Corps (Hancock's) stretched along the crest on the left of the Cemetery Hill, with the Third Corps (Sickles') on its left."

Major General David Birney, one of General Sickles Division commanders would add to the description of how the 3rd Corps troops fell into place covering the end of Cemetery Ridge as it terminated at the Round Tops. He would also note what occurred when Sickles, already unhappy with his position, heard of the initial fighting in his front. "At 7 a.m., under orders from Major-General Sickles, I relieved Geary's division, and formed a line, resting its left on the Sugar Loaf Mountain and the right thrown in a direct line toward the cemetery, connecting on the right with the Second Division of this corps. My picket line was in the Emmitsburg road, with sharpshooters some 300 yards in advance.

At 12 n., believing from the constant fire of the enemy that a movement was being made toward the left, I received permission from Major-General Sickles to send 100 of Berdan's Sharpshooters, with the Third Maine Regiment as a support, and feel the enemy's right. I sent Capt. J. C. Briscoe, of my staff, with the reconnaissance, which was under Colonel Berdan's command. They advanced from the peach orchard out the Millerstown road, and entered the woods in order to flank the enemy. The skirmishers of the enemy were driven in, but three columns of their forces were found marching to our left. The force sent by me was driven back by overwhelming numbers, with the loss of about 60, killed and wounded."

Berdan's men and those of the 3rd Maine had collided with Confederate Brigadier General Cadmus Wilcox's Alabamians who had been moving to assume their place in the Southern battle line. General Wilcox would report, "Not knowing whether the woods against which the right of my line was to rest was occupied by the enemy, the Tenth Alabama Regiment (Colonel Forney) was ordered to occupy the woods, and the Eleventh Alabama Regiment (Colonel Sanders) formed in line in the open field to the left of the Tenth.

The regiments, being preceded by skirmishers, were ordered to advance, the Eleventh to its position in line in rear of a fence, and the Tenth to keep on a line with the Eleventh, to protect it from the enemy's fire should he be found in the woods, the remaining regiments being held in rear till it should be ascertained if the enemy were in the woods.

The Eleventh advanced more easily than the Tenth, being in the open field. Having moved forward about 300 yards, this regiment received a heavy volley of musketry on its right flank and rear from the enemy, concealed behind ledges of rock and trees in the woods on its right. The Tenth Alabama moved forward promptly, and soon encountered a strong line of skirmishers. These were driven back upon their supports, two regiments of infantry--the Third Maine and the First New York [U.S.] Sharpshooters. A spirited musketry fight ensued between the Tenth Alabama and these two Federal regiments. Having continued for some fifteen or twenty minutes, Colonel Forney gave the command to charge, and led his regiment in person. This broke the enemy's line, and they fled precipitately from the woods, leaving 20 or 25 dead and twice that number wounded and prisoners.

In this affair, so creditable to the Tenth Alabama and its gallant colonel, this regiment lost 10 killed and 28 wounded. In the Eleventh Alabama, 1 officer (Major [R. J.] Fletcher) severely wounded, and 17 men wounded; 6 or 8 severely."

Union General Birney would mention this conflict to his commanding officer who became convinced that the Confederate assault would target the ground his men held. General Birney continued in his report discussing his commanders orders to move to a position General Sickles believed more favorable for defense. "Communicating this important information to Major-General Sickles, I was ordered by that officer to change my front to meet the attack. I did this by advancing my left 500 yards, and swinging around the right so as to rest on the Emmitsburg road at the peach orchard...My line was formed with Ward on the left, resting on the mountain, De Trobriand in the center, and Graham on my right in the peach orchard, with his right on the Emmitsburg road. Smith's battery of rifled guns was placed so as to command the gorge at the base of the Sugar Loaf Mountain;..."

General Meade would say of this advance, a movement he had not ordered, "About 3 p.m. I rode out to the extreme left, to await the arrival of the Fifth Corps and to post it, when I found that Major-General Sickles, commanding the Third Corps, not fully apprehending the instructions in regard to the position to be occupied, had advanced, or rather was in the act of advancing, his corps some half a mile or three-quarters of a mile in front of the line of the Second Corps, on the prolongation of which it was designed his corps should rest. Having found Major-General Sickles, I was explaining to him that he was too far in advance, and discussing with him the propriety of withdrawing, when the enemy opened on him with several batteries in his front and on his flank, and immediately brought forward columns of infantry and made a most vigorous assault. The Third Corps sustained the shock most heroically."

Second Corps commander General Winfield Scott Hancock, whose men had been immediately to Sickles' right before this advance, would look at the gap between his men and those of General Sickles and lament of the change, "The Third Corps having advanced far beyond the original line of battle, and Caldwell's division having been detached, a large interval remained on the left of the Second Division without troops."

Thus the movement of Southern troops to his left, the brief fighting in the woods to his front, and the perceived poor position for artillery on the ground originally assigned contributed to General Sickles decision to advance his men westward to form a new line, quite alone and away from immediate support. And so the stage was set for the fiercest fighting to occur during the colossal three day battle. [5]