The Rockpile (also known as Elliot Combat Base) and known in Vietnamese as Thon Khe Tri, is a solitary karst rock outcropping north of Route 9 and south of the former Vietnamese Demilitarized Zone (DMZ). Its relatively inaccessible location, reached only by helicopter, made it an important United States Army and US Marine Corps observation post and artillery base from 1966 to 1969.