From the Shiloh National Cemetery info

In 1866, the War Department established a cemetery on the battlefield of Shiloh, in southwestern Tennessee. In order to bury the dead not only from the April 6-7, 1862, battle of Shiloh but also from all the operations along the Tennessee River, workers began building the “Pittsburg Landing National Cemetery.” Changed to “Shiloh National Cemetery” in 1889, the cemetery holds 3,584 Civil War dead, 2,359 of them unknown. In the fall of 1866, workers disinterred the dead from 156 locations on the battlefield, and 565 different locations along the Tennessee River. Headboards of wood first marked each grave, but were replaced in 1876 and 1877 by granite stones. Tall stones marked the known dead and square, short stones denoted unknown soldiers.[u][/u]