[1] In 1778, John Parke Custis purchased an 1,100-acre (450 ha) tract of forested land on the Potomac River north of the town of Alexandria, Virginia.

To the west of Arlington House, tall grass and low native plants led down a slope into a natural area of close-growing trees the Custises called "the Grove.

"[2] About 60 feet (18 m) to the west of the flower garden, "the Grove" contained tall elm and oak trees which formed a canopy.

's daughter, Mary Anna Randolph Custis, married Robert E. Lee, an impoverished lieutenant in the United States Army, in June 1831.

[6] Realizing Union forces were likely to seize her home, Mary Custis Lee packed up most of her belongings and fled to her family estate at Ravensworth on May 17.

[8] On July 16, 1862, the United States Congress passed legislation authorizing the U.S. federal government to purchase land for national cemeteries for military dead, and put the U.S. Army Quartermaster General in charge of this program.

Quartermaster General Montgomery C. Meigs ordered that an examination of eligible sites be made for the establishment for a large new national military cemetery.

[9] The property was high and free from floods (which might unearth graves), it had a view of the District of Columbia, and it was aesthetically pleasing.

Its flower beds and paths had been trampled out of existence by troops and pack animals, and some of its trees had been cut down.

[1] That year, Meigs decided to build a monument to Civil War dead in the center of "the Grove".

Some of the dead had been interred on the battlefield, but most were full or partial remains discovered unburied on the field of battle.

[17] U.S. Army engineers chopped down the trees in eastern half of "the Grove", leaving only a small copse to the west.

[1] Meigs designed[18] a 6-foot (1.8 m) tall, 12-foot (3.7 m) long, 4-foot (1.2 m) wide grey granite and concrete cenotaph to rest on top of the burial vault.

On the west face was an inscription describing the number of dead in the vault below, and honoring the "unknowns of the Civil War".

The memorial was also raised off the earth onto a slightly larger base of rough-hewn dark grey granite blocks mortared together.

Four light grey granite sections about 6 to 9 inches (15 to 23 cm) high sat atop the original sides, decorated with pilasters.

The Civil War Unknowns Monument was the inspiration for Montgomery Meigs' own tomb, also located at Arlington National Cemetery.