The entire surface of the Park consists of low ridges and intervening valleys, beginning on the north in Herr’s Ridge, upon which Heth’s Division was deployed at the opening of the battle on July 1st. Opposite this ridge, and extending in the same direction, is McPherson Ridge, where the Union cavalry forces under Buford were deployed. Along Willoughby Run, which flows between these ridges, the battle opened on July 1, 1863. The next elevation, immediately north and west of the town, is known as Oak Ridge at its northern extremity and as far south as the Chambersburg Pike; from this point to its southern extremity it is called Seminary Ridge, taking its name from the yet existing Lutheran Theological Seminary. It was held by the Union Army on the first day of the battle and formed its principal line of defence. On the second and third days it was the principal Confederate line. Seminary Ridge at its southern extremity drops off to a small ravine beyond which is Warfield Ridge, which extends in a southerly direction opposite Big Round Top; this formed the right of the Confederate line of battle on the second and third days. South and southwest of the town is Cemetery Ridge, of which Big Round Top and Little Round Top are spurs, named from the Evergreen Cemetery and the site of the National Cemetery after the battle. [Illustration: Ricketts’ Battery.—Ricketts’ Battery on East Cemetery Hill was remanned four times. Owing to the slope, the guns could not be sufficiently depressed, and the defenders fought with sticks and stones] Cemetery Ridge formed the main line of battle of the Union Army during the battles of the 2nd and 3rd. A short distance east of the cemetery it bends sharply to the right, forming two rocky and wooded prominences, Culp’s Hill and Spangler’s Hill. Between Seminary Ridge on the west and Cemetery Ridge on the east, a low ridge along the line of the Emmitsburg Road is designated Emmitsburg Road Ridge. This extends to the Peach Orchard. It was crossed on the afternoon of the 3rd by the assaulting column of Pickett’s Charge, and is one of the interesting points of the battle. Another ridge on the west front of Little Round Top contains Devil’s Den, a mass of enormous granite rocks, apparently tossed in confusion by some giant hand. In this picturesque spot Longstreet made his famous assault against the Union left on the afternoon of July 2nd. The trend of these various ridges conforms generally to that of the Blue Ridge. [Illustration: Guns Supporting Pickett’s Charge.—These guns took part in the great artillery duel which preceded Pickett’s Charge]