While these struggles were going on in the border commonwealths, the Union soldiers lay inactive along the Potomac. Constant drill had changed the mob into some semblance of an organized army, but the careful Scott feared to risk a general engagement. The hostile forces stretched in three pairs of groups across Virginia from northwest to southeast. In the southeastern part of the State, at Fortress Monroe, Butler faced the Confederate Magruder. At Manassas, opposite Washington, and about thirty miles southwest, lay a Confederate army under General Beauregard. General Patterson, a veteran of the War of 1812, commanded considerable forces in Southern Pennsylvania. About the middle of June he advanced against Harper's Ferry, which had been abandoned by the Unionists the latter part of April and was now occupied by General Joseph E. Johnston. Johnston evacuated the place upon Patterson's approach, and retreated up the Shenandoah Valley, in a southwesterly direction, to Winchester. Patterson followed part way, and the two armies now lay watching each other. Anxious to see the rebellion put down by one blow, the North was becoming impatient. "On to Richmond!" was the ceaseless cry. Yielding to this, Scott ordered an advance. July 16th, General McDowell, leaving one division to protect Washington, led forth an army 28,000 strong to attack the enemy at Manassas. He advanced slowly and with great caution. The enemy were found posted in a line eight miles long upon the south bank of Bull Run, a small river three miles east of Manassas, running in a southeasterly direction. Several days were spent in reconnoitering. Meanwhile, Johnston, whom Patterson was expected to hold at Winchester, had stolen away to join Beauregard, their combined forces numbering about 30,000. McDowell was ignorant of Johnston's movement, supposing him still at Winchester. [Illustration: Portrait.] General Irvin McDowell. On the morning of the 21st McDowell advanced to the attack. Beauregard held all the lower fords, besides a stone bridge on the Warrenton turnpike which crosses the river at right angles. Two divisions, under Hunter and Heintzelman, were set in motion before sunrise to make a flanking detour and cross Bull Run at Sudley's Ford, some distance farther up. To distract attention from this movement, Tyler's division began an attack at the stone bridge. This was held by a regiment and a half, with four guns, under General Evans. He replied vigorously at first, but perceiving after a while that Tyler was only feigning, and learning of the flank movement above, he left four companies at the bridge and drew up the rest of his forces on a ridge north of Warrenton turnpike to await Hunter and Heintzelman's approach down the Sudley road. [Illustration: Portrait.] General Samuel P. Heintzelman.