There are fourteen Headquarters markers on the Gettysburg battlefield. These are cannon barrels that have their breeches planted in a masonry base and their barrels pointed at the sky. There is one for each army headquarters and each of their infantry Corps, as well as the corps-sized Artillery of the Army of the Potomac:

Four Confederate markers: Army HQ, and three Corps HQ
Eight Union markers: Army HQ, eight Infantry Corps HQ (with two for the two commanders of the First Corps), and Chief of Artillery HQ. There is no HQ marker for the Union Cavalry Corps.

The markers were designed by Emmor Bradley Cope for the War Department. Cope started out the war as a private in the First Pennsylvania Reserves, transferred to Battery C, 5th U.S. Artillery, and ended the war as aide-de-camp to Major General Gouverneur K. Warren. He created a survey of the battlefield in August of 1863 and eventually became Topographical Engineer of the Gettysburg National Park Commission. He was appointed the first park superintendant in 1904.

Confederate Headquarters Markers

	General Robert E. Lee Army of Northern Virginia		Lieutenant General James Longstreet First Corps
	Lieutenant General Richard S. Ewell Second Corps		Lieutenant General Ambrose P. Hill Third Corps

Union Headquarters Markers

	Major General George Mead Army of the Potomac		Major General Abner Doubleday First Corps (July 1)
	Major General John Newton First Corps (July 2-3)		Major General Winfield S. Hancock Second Corps
	Major General Daniel E. Sickles Third Corps		Major General George Sykes Fifth Corps
	Major General John Sedgwick Sixth Corps		Major General Oliver O. Howard Eleventh Corps
	Major General Henry W. Slocum Twelfth Corps		Brigadier General Henry J. Hunt Chief of Artillery