A 1930s proposal to recycle Civil War-era military roads and forts into a circumferential roadway would have adapted military artifacts to address expanding civilian needs. The circular scheme is reprised in the 64-mile long I-495, the Capital Beltway (1961-4). Its origins as a National Defence Highway designed to move military equipment and personnel, and allow mass evacuation of the city in the event of nuclear attack required that its diameter exceed a thermonuclear detonation centered on the capital.