The army of the Union, called the Army of the Potomac, assembled at Arlington Heights and Alexandria. General McDowell was placed in command. Half of his soldiers were men who had enlisted for three months, who had suddenly left their homes at the call of the President. Their term of service had nearly expired. The three years' men had been but a few days in camp. Military duties were new. They knew nothing of discipline, but they confidently expected to defeat the enemy and move on to Richmond. Few people thought of the possibility of defeat. Let us walk up the valley of Bull Run and notice its fords, its wooded banks, the scattered farm-houses, and fields of waving grain. Ten miles from the Occoquan we come to the railroad bridge. A mile farther up is McLean's Ford; another mile carries us to Blackburn's, and another mile brings us to Mitchell's. Above these are Island Ford, Lewis Ford, and Ball's Ford. Three miles above Mitchell's there is a stone bridge, where the turnpike leading from Centreville to Warrenton crosses the stream. Two miles farther up is a place called Sudley Springs,--a cluster of houses, a little stone church, a blacksmith's shop. The stream there has dwindled to a brook, and gurgles over a rocky bed. Going back to the stone bridge, and standing upon its parapet, you may look east to Centreville, about four miles distant, beautifully situated on a high ridge of land, but a very old, dilapidated place when you get to it. Going west from the bridge, you see upon your right hand a swell of land, and another at your left hand, south of the turnpike. A brook trickles by the roadside. Leaving the turnpike, and ascending the ridge on the north side, you see that towards Sudley Springs there are other swells of land, with wheat-fields, fences, scattered trees, and groves of pines and oaks. Looking across to the hill south of the turnpike, a half-mile distant, you see the house of Mr. Lewis, and west of it Mrs. Henry's, on the highest knoll. Mrs. Henry is an old lady, so far advanced in life that she is helpless. Going up the turnpike a mile from the bridge, you come to the toll-gate, kept by Mr. Mathey. A cross-road comes down from Sudley Springs, and leads south towards Manassas Junction, six miles distant. Leave the turnpike once more, and go northwest a half-mile, and you come to the farm of Mr. Dogan. There are farm-sheds and haystacks near his house. This ground, from Dogan's to the ridge east of the toll-gate, across the turnpike and the trickling brook to Mr. Lewis's and Mrs. Henry's, is the battle-field. You see it,--the ridges of land, the houses, haystacks, fences, knolls, ravines, wheat-fields, turnpike, and groves of oak and pine,--a territory about two miles square. On Saturday, June 20th, General Johnston, with nearly all the Rebel army of the Shenandoah, arrived at Manassas. Being General Beauregard's superior officer, he took command of all the troops. He had about thirty thousand men.