The significance of the geography of the Gettysburg battlefield is even more interesting when you consider that neither army intended to fight a battle there. General Robert E. Lee, upon learning the Army of the Potomac was north of its namesake river on June 28, 1863, ordered the Army of...
The significance of the geography of the Gettysburg battlefield is even more interesting when you consider that neither army intended to fight a battle there. General Robert E. Lee, upon learning the Army of the Potomac was north of its namesake river on June 28, 1863, ordered the Army of Northern Virginia to concentrate around Cashtown, some eight miles west of Gettysburg and, more importantly, behind the ridge of South Mountain. Union General George G. Meade, who had just been ordered to take command of the Army of the Potomac that day, preferred a defensive position along Pipe Creek in Maryland, a day's march to the south of Gettysburg and a better location in which he could cover Washington.
The ridges west of Gettysburg—from west to east, Herr Ridge, McPherson's Ridge, and Seminary Ridge—all ran north to south and provided good delaying positions for General John Buford's Union cavalry when the Confederate division of Henry Heth, moving toward Gettysburg to collect supplies, particularly a large stock of shoes, blundered into them on the morning of July 1. General John F. Reynolds, commanding the Union I Corps racing to support Buford, was really the one that forced the battle to be fought where it was by committing first his troops and then the arriving troops of General Oliver Howard's XI Corps.
Howard, recognizing the defensive value of Cemetery Hill south of the town, had the prescience to post artillery and some reserve troops there, which gave the Union forces a fallback position later in the afternoon. Reynolds was killed in the opening moments of the battle, leaving Howard the senior commander on the field; the commander of the II Corps, General Winfield Scott Hancock, was ordered by Meade to take command of the situation despite being Howard's junior. Hancock diplomatically agreed with Howard's dispositions on Cemetery Hill, which gave the Union a safe rallying position when their lines, facing west, were caught in the flank by the Confederate II Corps arriving on the scene from the north.
The Union line from the evening of July 1 stretched from Culp's Hill just to the east of Cemetery Hill, south along Cemetery Ridge, which gradually lowered until rising again and ending at two wooded hills known as Big and Little Round Top. This position, which resembled a fishhook, gave the Army of the Potomac interior lines—reinforcements arriving from the south could be directed quickly to any part of it or could be moved with relative easy from one part to another. The Army of Northern Virginia, by comparison, had a much longer line to cover, and any shifting of forces would have to travel a greater distance.
The only real weakness in the Union line on July 2 was at the southern, lower section of Cemetery Ridge, and it was here that Confederate General James Longstreet intended to carry out a flanking attack that would push the Union forces out of their strong position closer to the town. However, General Daniel Sickles, commanding the Union III Corps on this part of the line, took it upon himself to move his troops forward, or westward, to somewhat higher ground, which inadvertently spoiled Longstreet's plan. Even though Sickles's move was generally dumb—in moving forward, his troops became disconnected from the rest of the line—when the Confederates launched their attack, they were surprised to find Union forces in their way. Sickles's new position crumbled under the assault, but caused enough of a delay to allow Hancock to rush reinforcements to the exposed area of Cemetery Ridge and eventually repel the Confederates. Similarly, another Confederate attack later in the day on the other end of the Union line, directed at Culp's and Cemetery hills, was also beaten back; the Union forces occupied too strong a position, forcing the Confederates to fight uphill. More importantly, the Union forces had the advantage of being able to shift reinforcements rapidly behind the ridge and hills.
Having attacked both ends of the Union line and failed, Lee felt his last option was to try the center of the Union position—a massive frontal assault by 15,000 men, known to posterity as Pickett's Charge. Here the terrain also played a deciding role, but in an unusual way. Contrary to popular belief, the attack was not necessarily doomed and could have succeeded. The assault was preceded by an hour-long artillery bombardment of the Union lines, which should have wrecked the Union artillery and caused losses among the defending infantry.
However, it is an odd feature of the battlefield that from the vantage point of the Confederate position on Seminary Ridge, Cemetery Ridge appears higher than it actually is. As a result, most of the Confederate artillery fire overshot the Union line, wreaking havoc in its rear area but sparing the Union artillery and infantry. To conserve ammunition for the coming attack and to fool the Confederates into thinking their fire had been more effective than it was, Meade's artillery chief General Henry Hunt ordered his batteries to stop firing and even made a show of pulling some of them out of line. When the Confederates advanced, these quickly returned to their positions and poured a murderous fire into the attacking columns. Although the Confederates fought ferociously, a few of them reaching and briefly breaking through the Union line, the assault was repulsed, with barely 5,000 of the original 15,000-man attacking force making it back to the Confederate lines.