The Thang Long Imperial Citadel was built in the 11th century by the Ly Viet Dynasty. It was constructed on the remains of a Chinese fortress dating from the 7th century. The centre of regional political power for almost 13 centuries without interruption.
On the card you see the 33 m tall Hanoi Flag Tower, built in 1812 as an observation post to the Hanoi Citadel.
The stamp depicts another UNESCO World Heritage site: Complex of Hué Monuments.