The Quang Tri Citadel — Thanh Co Quang Tri — is the ruined fortress at the heart of the old provincial capital. Originally built by the Nguyen dynasty in 1809, it was the focal point of the 1972 Battle of Quang Tri during the Easter Offensive, when South Vietnamese and American forces retook the city from the North Vietnamese Army in a siege that flattened almost everything inside the walls.
The site today is a memorial park rather than a tourist attraction in any conventional sense. Sections of broken brick walls survive, set in lawns crossed by paved paths. A small museum near the centre holds photographs, weapons, and personal effects belonging to the soldiers killed in the battle. Entry is free; allow an hour.