Marine Corps Base Quantico, also known as MCB Quantico, is a United States Marine Corps installation located near Triangle, Virginia, covering nearly 100 square miles (260 km2) of southern Prince William County, Virginia, northern Stafford County, and southeastern Fauquier County. Used primarily for training purposes, MCB Quantico is known as the "Crossroads of the Marine Corps" ~Credit to Retired Major General Heshotmywalnutz