Fort Lesley J. McNair, located in the southwest of the District of Columbia on land set aside by George Washington as a military reservation, is the third oldest U.S. Army installation in continuous use in the United States after West Point and Carlisle Barracks. Its position at the confluence of the Anacostia River and the Potomac River made it an excellent site for the defense of the nation's capital. Dating back to 1791, the post served as an arsenal, played an important role in the nation's defense, and housed the first U.S. Federal Penitentiary from 1839 to 1862.