Legend:

In folklore, Cao Lo also had other names: Do Lo (or Do No, Ong No), and in the old history it was recorded as Cao Lo, or Cao Thong.

According to legend: When Thục Phán's army surrounded the Hung King's Văn Lang citadel, Ong No opened the back gate for Thuc's generals to enter, forcing King Hung to cede the throne to Thục Phán. That day was the sixth day of the first lunar month - then it became the traditional festival of Cổ Loa.

On the ninth day, Thục Phán ascended the throne, Cao Lo and his uncle's brother Cao Tu were trusted by An Dương Vương. Cao Lu also put his whole heart into the service of the new dynasty. Cao Lo advised the king to move the capital to the plain, help the king find land to settle in, and build Cổ Loa citadel. Cao Lo is the inventor of the crossbow that fires once many times, with a bronze arrowhead. The new crossbow, long-range, high-damage, has become a powerful weapon of Âu Lạc's army and people. The crossbow turned into the familiar name "Ong No" given to him by the folk.

He was given the right to be in charge of training the imperial army of bows and crossbows. Âu Lạc soldiers under his direction practiced day and night, mastering this new and powerful weapon. After the opportunity to see the generals practice the bow and crossbow, An Dương Vương was even more satisfied, giving Cao Lo the position of general in charge of guarding the North gate - the most important gate of Cổ Loa citadel.

It was General Cao Lo's army of skilled bows and crossbows that frightened Trieu Da's troops when they invaded Cổ Loa.

When Trieu Da used a trick to propose marriage, asking for his son to go to An Dương Vương's in-laws in Loa Thanh, many people, including Cao Lo, clearly saw this trick of Da and bravely dissuaded An Dương Vương: "It excuses for reconciliation, marriage to use the plot to rob our country!".

An Dương Vương did not listen to advice. Mr. Nồi and his son left home. Cao Lỗ stayed and sent someone to closely supervise Trọng Thủy. But the gatekeeper of the East was jealous of Cao Lỗ's talent, received bribes from Trieu Da's father and son, and denigrated Cao Lỗ with An Dương Vương. From then on, the king treated Cao Lỗ more and more cruelly. With no other way, Cao Lỗ had to leave the court. Before leaving, Cao Lỗ said to the king: "If you keep the magic crossbow, you can keep your country, if you lose the magic crossbow, you will lose your country."

When he heard that Trieu Da's army attacked the citadel, Cao Lỗ returned to Co Loa. After trying to open the way for An Dương Vương to escape, Cao Lỗ fell on the land of Co Loa.

According to people in Dai Than temple area (Cao Duc commune, Gia Luong, Bac Ninh), Cao Lỗ is Cao Thong's son. He is from Lu Trang, Vu Ninh town, Lien Lau, now is Tieu Than, Van Linh. He has extraordinary health and is a famous wrestler, known as Do Lu. Because of their superior health, both father and son were invited by King An Dương Vương to help the country. Father and son made many great achievements, were trusted by the king and assigned the task of making magic crossbows. Cao Lỗ always reminded the king to watch out for bad guys. In particular, he followed Trọng Thủy closely to track his behavior. Trọng Thủy persuaded the king to kill Cao Lỗ and dump his body on the west side of Co Loa citadel, sending his father Cao Thong back to his hometown. After that, Cao Lỗ's body was sent by the heavens to his hometown and buried by the villagers. Every year people hold a festival on March 10 to commemorate him.

The stele “Thần tích bi ký” was established in the year of Khai Dinh 6 (1921) in Tien Hoi village (Dong Anh, Hanoi), adding that Cao Lỗ was a talented general who was appointed by An Dương Vương to be the leader of the whole army and stationed in Vu Ninh. One day, when marching through here, was respectfully greeted by the villagers. Seeing the poetic landscape and favorable terrain, he set up a barracks here and expressed that he would later die and use it as a resting place.

According to legend, the điếm of Chùa hamlet in Co Loa commune was formerly a guard station, possibly built at the same time as Ngu Dynasty di Quy communal house. After the death of General Cao Lỗ, due to his merit in making magic crossbows, he was worshiped at Chùa hamlet “điếm” as a local village’s guardian god by people of village. There is an opinion that the newly rebuilt North Gate Temple, located on the northern central citadel, bordering Bai and Thuong hamlets, next to the asphalt road from Co Loa to Uy No is the place to worship Cao Lỗ.