...y sun, two weeks later, his approach was the signal for the Union troops at Martinsburg, under Sigel, to fall back across the Potomac to Maryland Heights. The road to Washington was thus blocked at Harper's Ferry , where Early intended to cross. He therefore was compelled to get over at Shepherdstown, while Breckenridge engaged Sigel at Harper's Ferry. Once across the river, Early's scouting parties quickl...