Location

Known as the oldest citadel in Vietnam, Co Loa citadel is dated to the third century BC and was the capital of the ancient Au Lac country. Therefore, this place is associated with many legends of Vietnam such as: King An Duong Vuong was supported by the god Kim Quy to get a magic crossbow to defeat the enemy defending the citadel, the tragic love story of princess My Chau and prince Trong Thuy… Although it is only a legend, it is considered as a spiritual “food” that has entered the subconscious of Vietnamese people for many generations.

1. Location of Co Loa
Co Loa is located in a rather favorable position, at the top of the triangle of the Red River Delta – the lifeblood in waterways and roads, besides, it is also possible to easily control the surrounding plains and mountains from here. Therefore, in the Au Lac period, this position was considered the most favorable position for the largest center of power.

Another special feature of the location of Co Loa citadel is that the citadel is located on the left bank of the Hoang River on high hilly land. This not only helps Co Loa land receive yearly fertile alluvial deposits, but also avoids flooding. Although the Hoang River is not a big river, it acts as a bridge connecting the Red River with the Cau River. This is not only meaningful in accreting alluvium to help people develop agriculture, but is also helpful in the military when controlling the waterway network of the Red and Thai Binh rivers and also playing a dominant role in the waterway network of the whole Northern Vietnam.

2. Summary of Co Loa citadel structure
In the history of Vietnam, there is no shortage of citadel works, but only Co Loa citadel is considered to be the oldest citadel, the largest scale and also has the most unique structure in the history of citadel construction of the ancient Vietnamese. Why is that so?
Co Loa citadel was not only built in a prime location but also impressed scientists by its unique and delicate features when building the citadel. The ancient Vietnamese knew how to harmonize the natural terrain with artificial construction. Scientists have shown that the ancients knew how to take advantage of the height of the hills to make the foundation of the outer wall, using the surrounding Hoang River as a natural moat, Dam Ca was used as a wharf port to trade goods. Even the choice of building materials was cleverly used by the ancients to create solidity for the wall. Soil is the main material followed by broken stone and ceramic. The riverside and lagoon sections are embanked with large boulders and cobblestones interspersed with a large amount of broken pottery to help prevent the wall from collapsing. This is evidenced by the fragments of the city that are still intact to this day.

Co Loa Citadel, although there is no specific diagram still preserved, but according to archaeologists, they found that the citadel has 3 rings, in which the inner citadel was built in the later Ngo Quyen period.
• The inner citadel is rectangular, with an average height of 5m above the ground, the wall is 6-12m wide, the foot is 20-30m wide, the circumference is 1,650m and there is a door looking into the Ngu Trieu Di Quy architectural building.
• The middle citadel is a circular citadel without a symmetrical shape, 6,500 m long, 10 m high at the top, 10 m wide on average, with four gates in the east, north, northwest and southwest directions, in which the East gate connects to the Red River.
• The outer citadel also has no clear shape, more than 8,000m long, with an average height of 3–4 m (more than 8m in some places).
To ensure the best offensive defense, the ancients interwoven moats around the outside of each citadel. Each moat is about 10m to 30m wide and connects to the Hoang River.
It can be said that Co Loa is not only a royal citadel but also a military citadel and also a city. Because this is not only the place where the headquarters apparatus is located with the “trimeric citadel” but also the fortified walls have created a military base that is difficult to take down. Especially, the use of rivers and lagoons has created a busy trading point for goods under Au Lac’s time until later.
From the above, Co Loa is an ancient citadel – a relic worth exploring for tourists. The article gets reference materials from websites, newspapers, and radio.
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