But at the Battle of Gettysburg, Ewell's military reputation started a long decline. On July 1, 1863, Ewell's corps approached Gettysburg from the north and smashed the Union XI Corps and part of the I Corps, driving them back through the town and forcing them to take up defensive positions on Cemetery Hill south of town. Lee had just arrived on the field and saw the importance of this position. He sent discretionary orders to Ewell that Cemetery Hill be taken "if practicable." Historian James M. McPherson wrote, "Had Jackson still lived, he undoubtedly would have found it practicable. But Ewell was not Jackson." Ewell chose not to attempt the assault.