This 1863-built earthwork is one of two remaining in Manassas – the other being the Confederate-built Mayfield Earthwork Fort (1861) about four miles east. Named for a nearby stream, Cannon Branch was one of several earthwork forts built alongside the Orange & Alexandria Railroad to protect the rail line that carried supplies to the Union Army. Today, the area includes 11 acres and is free to the public, open from dawn to dusk.