From 1808 the grove witnessed approximately fifty duels by gentlemen, military officers, and politicians, settling "affairs of honor". A formalized set of rules dealing with dueling etiquette referred to as a Code duello was usually enforced by the duelers and their seconds, even though dueling was illegal in the District of Columbia, and in most American states and territories.
Following the Civil War, dueling fell out of favor as a means of settling personal grievances and declined rapidly; the last known duel was fought here in 1868.
In 1819, Colonel John Mason McCarty killed his second cousin, General Armistead Thomson Mason. McCarty was haunted for years by his experience after surviving the musket duel.
Jonathan Cilley, a Representative from Maine, was a reluctant participant. In February 1838, Cilley was killed by Congressman William J. Graves of Kentucky. Graves was a stand-in for New York newspaper editor James Webb, whom Cilley had called corrupt. Cilley was inexperienced with guns, and Graves was allowed to use a powerful rifle. A severed artery in Cilley's leg caused him to bleed to death in ninety seconds. This duel prompted passage of a Congressional act of February 20, 1839, prohibiting the giving or accepting challenges to a duel within the District of Columbia.
Hauck, Dennis William, Haunted Places, The National Directory
Holland, Barbara, Gentlemen's Blood: A History of Dueling from Swords at Dawn to Pistols at Dusk