High Quality Content by WIKIPEDIA articles! The First Day of the Battle of Gettysburg during the American Civil War took place on July 1, 1863, and began as an engagement between isolated units of the Army of Northern Virginia under Confederate General Robert E. Lee and the Army of the Potomac under Union Maj. Gen. George G. Meade. It soon escalated into a major battle which culminated in the outnumbered and defeated Union forces retreating to the high ground south of Gettysburg, Pennsylvania.