Cổ Loa Citadel
Cổ Loa Citadel (Vietnamese: Thành Cổ Loa) is an important fortified settlement and archaeological site in present-day Hanoi's Dong Anh district, about 16 kilometers (10 mi) northeast of Hanoi city center. Various relics of the Bronze Age Phung Nguyen culture and Dong Son culture have been found in Cổ Loa, although it was later established as the capital of Âu Lạc Kingdom during the 3rd century BC (about 257 BCE).  Further construction was added during the later dynasties. Cổ Loa remained an important political center of the Vietnamese people until the 10th century. The name "Cổ Loa" is derived from the Sino-Vietnamese 古螺, meaning "old spiral", reflecting its multi-layered structure of earthworks, moats and ditches.
According to folklore, Thục Phán defeated the last of the Hung kings in 257 BCE and founded the kingdom of Âu Lạc, choosing the site of Cổ Loa as his capital. Given its relatively large size, Cổ Loa maintained its dominant presence in the northern floodplain of the Red River Delta and would have required a large amount of labour and resources to construct.
The mythical story goes that when the fortress was being built, all the work done during the day was mysteriously destroyed at night. The king made a sacrifice to the gods and in one night, a golden turtle appeared to him in a dream and told him the fortress was built on the turtle's carapace. The king was instructed to build the city in a new location, that of present-day Cổ Loa. The king did so, and the city was soon finished.
Out of gratefulness to the king, the magic turtle gave the king a claw that he could use as a trigger on his crossbow. When used, it multiplied its force by the thousands. However, one of the Qin dynasty general, Zhao Tuo, took advantage of the decline of the Qin and created his own kingdom north of Âu Lạc called Nanyue. He tried to conquer his southern neighbour but was defeated. Instead, he married his son to the daughter of the Thục Phán. When the son was in Co Loa, he discovered the magic turtle's claw and stole it. His father then proceeded to invade Âu Lạc and easily defeated it.
Stories of the Thục Phán's demise vary. Some say he committed suicide by jumping in the ocean. Some say he was borne off to sea by the magic turtle to never be seen again. In some versions, he was told by the magic turtle about his daughter's betrayal and killed his own daughter before killing himself.
The site consists of two outer sets of ramparts and a citadel on the inside, of rectangular shape. The moats consist of a series of streams, including the Hoang Giang River and a network of lakes that provided Cổ Loa with protection and navigation.
The outer rampart comprises a perimeter of 8 km and is lined with guard towers. The ramparts still stand up to 12 m high and are 25 m in width at their base. Besides, part of the inner rampart was cut through for the purpose of archaeological investigation, which was dated from 400-350 BC.And it was suggested that this rampart was constructed by a local and indigenous society prior to the colonization of Han dynasty. Also, archaeologists have estimated that over two million cubic metres of material were moved in order to construct the entire fortress, including moats that were fed by the Hoang River.
Then in 2007 - 2008 another excavation took place that excavated the middle wall of Co Loa citadel. The excavation cut through the entire width of the rampart. The stratification showed multiple layers of construction deposits: three periods and five major phases of construction.
Excavations made by archaeologists have revealed Dong Son style pottery that had stratified over time under the walls, while a drum was found by chance by Nguyen Giang Hai and Nguyen Van Hung. The drum included a hoard of bronze objects. The rarity of such objects in Southeast Asia and the range found at Co Loa is believed to possibly be unique.
The drum itself is one of the largest Bronze Age drums to have been recovered from the Red River Delta, standing 57 cm high and boasting a tympanum with a diameter of 73.6 cm. The drum itself weighs 72 kg and contains around 200 pieces of bronze, including 20 kg of scrap pieces from a range of artefacts. These include socketed hoes and ploughshares, socketed axes, and spearheads.
The artifacts are numerically dominated by the ploughshares, of which there are 96. Six hoes and a chisel were in the set. There were 32 socketed axes of various shapes, including a boat shaped axehead. This was almost a replica to a clay mound found in the grave of the bronze metalworker at Lang Ca.
Sixteen spearheads, a dagger and eight arrowheads were also found. One spearhead generated special interest because it was bimetallic, with an iron blade fitting into a bronze socket.
Đông Sơn culture (700 BC - 100 AD)
- List of capitals of Vietnam
- Triệu dynasty
- Nam Việt
- Triệu Đà
- Phiên Ngung
- Trọng Thuỷ
- An Dương Vương
- Âu Lạc
- Tây Vu Vương
- Đông Sơn culture
- Bách Việt
- Ray (2010).
- Higham, p. 122.
- Truong Buu Lam, A Story of Vietnam
- Kim, N. C., Van Toi, L., & Hiep, T. H. (2010). Co Loa: an investigation of Vietnam's ancient capital.  Antiquity, 84(326).
- Kim, Nam; Lai Van Toi; Trinh Hoang Hiep (2010). "Co Loa: an investigation of Vietnam's ancient capital". Antiquity: 1011–1027.
- Higham, Charles (1996). The Bronze Age of Southeast Asia. Cambridge World Archaeology. ISBN 0-521-56505-7.
- Ray, Nick; et al. (2010), "Co Loa Citadel", Vietnam, Lonely Planet, p. 123, ISBN 9781742203898.