Today, June 25,1863, General Fighting Joe Hooker of the Union Army of the Potomac has now started to make a significant pursuit of the Confederates with the bulk of his army upon learning that the Confederate Army of Northern Virginia has crossed the Potomac River. He has ordered the Army of the Potomac to cross into Maryland and concentrate at Middletown (Slocum's XII Corps) and Frederick (the rest of the army, led by Reynolds's advance wing—the I, III, and XI Corps)
Meanwhile there are reports that:
Advanced Confederate troops in E. Rodes' Division (under Ewell) occupied Chambersburg in Pennsylvania and are marching eastward toward York, Pennsylvania.
Thus, long lines of troop both blue and gray are marching through Maryland in an almost parallel course in anticipation of a large battle somewhere in Pennsylvania or possible Maryland. Confederate forces under Lee invading Pennsylvania number approximately 75,000 and the Union forces in pursuit number approximately 100,000.
http://www.militaryhistoryonline.com/gettysburg/leemarch.aspx
