Washington Square, originally called Southeast Square, was one of five such plots included in William Penn's 1682 design for the city of Philadelphia. Twenty-five years later it became a potter's field. It served as a pasture briefly until 1776, when casualties of Washington's army, as well as some British prisoners of war, were buried there in long, deep pits where coffins were stacked one atop another. In 1793, victims of the fearsome yellow fever epidemic were added to the field's host of corpses. The square was subsequently closed to burials, but it and the surrounding neighborhood when Lewis saw them before and after the expedition were dismal and disreputable. The scene was refreshed in 1815 with the planting of some 60 varieties of trees sheltering meanders of public walkways. In 1825 it was renamed in honor of the great American general and first President.
Thereafter it suffered intermittent periods of comparative neglect until the middle of the twentieth century, when the Washington Square Planning Committee set about erecting a Revolutionary War memorial there. It was to contain the remains of an unknown Continental soldier who had died of wounds or illness. In November 1956, a search for appropriate remains found one that filled most of the requirements: it was from a mass grave and was the corpse of a man in his very early twenties with a "plow wound" that could have been produced by a musket ball. But since neither uniform nor buttons were present, the archaeologists were unable to confirm that the body was that of a soldier, and if a soldier, an American.1
1. John L. Cotter et al, The Buried Past: An Archaeological History of Philadelphia (Philadelphia: University of Pennsylvania Press, 1992), 205-10.