It was built together with Phuc Hoa, Lang Son, Dai La citadel by Governor Cao Bien under Duong Hy Ton dynasty when his army battled with An Nam.
Situated in Na Lu village, Hoang Tung commune, the citadel lies in the
national highway No203, in the Northwest of Cao Binh market. The
citadel has rectangular shape, four entrances North, South, East, and
West with 800 meters height and 600 meters width.
It was built
from wooden-hammer brick. Its foot was chocked by enormous and flat
carved stone. Its entrances were made from thick plank. Inside the
citadel, there are four emerging earth mouths named Dragon, Unicorn,
Tortoise, and Phoenix . The main earth mouth is the Dragon, which was
built in the main area of palace - the
King Le temple.
The highest emerging earth mouth is the Unicorn. The biggest one is the
Tortoise in the North of the citadel. The Phoenix earth mouth is in the
middle of the citadel. Lying along the East of the citadel, there are
lotus pond and chequered field.
