The Van Lang Kingdom of Lac Viet people in the Hung Vuong period, there were 15 states with the center located in the northern mountainous area. At the beginning of the 3rd century BC, a newly unified, grand, and powerful empire called the Qin dynasty - the empire in the north, waged a war of invasion on a large scale to the South, with the number of troops up to 50,000, led by Do Thu. Van Lang Kingdom was in danger.

Thuc Phan, who was a leader of Tay Au tribe in the northern area of Van Lang at that time, collaborated with many chieftains of Tay Au and Lac Viet to organize the resistance against the Qin army. During the war, Thuc Phan became a talented leader and gained considerable prestige of both Tay Au and Lac Viet people.

In 208 BC, after defeating the Qin army, Thuc Phan unified the two tribes of Lac Viet and Au Viet, formed the Kingdom of Au Lac. He proclaimed himself King An Duong Vuong, continued the throne from Hung King. It was an especially important event that marked the process of the unification of the tribes and demonstrated the new development of the ancient nation of the Vietnamese ethnic groups. The event also represented the succession at a higher level than Van Lang and an inevitable requirement of the history. An Duong Vuong decided to move the center of the country from the northern mountainous region to a larger and more favorable plain, established a new capital, and led the country against the foreign invaders. That area is Co Loa in present-day.

In a short time, An Duong Vuong and people of Au Lac Kingdom, constructed a huge and unique citadel, known as Oc, Tu Long Thanh, Loa or Co Loa. Co Loa Citadel had a strategic and geographic location for both defense and attack: two side were surrounded by impenetrable mountains and forests, and a river flowing by.

Co Loa Citadel, served as the capital of Au Lac Kingdom, had three functions: the capital, the fortress and the urban area. Many archaeologists rated it as the oldest, the most unique and the largest citadel in scale of all the Vietnamese citadels in the history.

Especially, Cao Lo – the weaponry engineer and minister built a crossbow called Lien Chau which could shoot thousands of arrows at once (known as the Magic Crossbow). It was considered the invincible divine weapon that protect Au Lac country from the invaders. There was a saying: "If the crossbow was safe, the country was safe; if it was lost, the country was lost ". Thanks to the strong citadel, deep trenches, powerful weapons and the solidarity of the army and people, An Duong Vuong repeatedly defeated the invading Trieu Da army and left many valuable lessons for the next generations about the country’s construction and defense.

Today, the Co Loa Heritage still preserves many decrees issued by the Le and Nguyen dynasties (from the 17th century to the beginning of the 20th century), bestowed upon Co Loa Commune to worship King An Duong Vuong. The decrees all honored An Duong Vuong as the king with many merits in building and protecting the country. In the decree compiled on April 20 of the 1st year of Duc Long (1629) wrote: An Duong Vuong was "a talented hero in the world, with the great mind and effort, he helped the country to be safe, maintain the Vietnamese land”

Every year, on the King’s birthday, the 11th of the eight lunar calendar which was recorded in the book “Ngọc Phả Cổ Lục”, the Thang Long - Hanoi Heritage Conservation Center and Management Department of Co Loa  vestige site  respectfully organize the incense offering ceremony to commemorate King An Duong Vuong at Thuong Temple in the Co Loa Heritage Site, Co Loa Commune, Dong Anh District, Hanoi, pay tribute to the ancestors, maintain the tradition “When you eat a fruit, think of the man who planted the tree”, and promote the tradition of the country’s renovation and construction.

MANAGEMENT DEPARTMENT OF CO LOA VESTIGE SITE