“Dai Nam Thuc luc Chinh bien” is a history book compiled by Quoc Su Quan (Office of National History) under the Nguyen dynasty. The part on Kings Gia Long, Minh Mang and Thieu Tri were written in 1848, recording the event when king Gia Long exercised sovereignty activities over the Hoang Sa Islands in 1816, the event when King Minh Mang built the temple, planted the stele, trees, conducted measurements and drew the map of these islands. The above-said events were written as follows:
In the year of Binh Ty, the dynastic title Gia Long the 15th (1816)….The king sent the naval force and the Hoang Sa boat team to Hoang Sa to explore the sea route:
In the year of Binh Than, the dynastic title Minh Mang the 17th (1836), the spring of January 1st….Bo Cong reports: the Border of our country’s sea area has Hoang Sa land which is very important and vulnerable. In the past a physical map was drawn, very large but not clear. Every year, people were sent to explore so as to learn the sea route. From this year on, when the end of January came, the naval force and the guards were to be sent on a boat to go to Quang Ngai in early February, asking Quang Ngai and Binh Dinh to lease 4 boats from the people to go to Hoang Sa island, to any island, any sandbank there; when the boats came, they started to measure the length and the width, the breadth and the height, the circuit of the island and the depth of the sea, the underground dumps, if any. And then they had to draw a map. They had to think about their departure date, which estuary they started, which direction they aimed to go to the island, then based on the route to estimate the length in miles. Then from the island to look towards the shore, aim straight to certain province, then change to stand squarely towards another province, to estimate the length from there to the shore. This must be carried out without delay and report it to the court”.
“The king having heard the report sent a naval force led by Pham Huu Nhat to go the island, bringing along 10 wooden boards so as to plant as marking board there (each board is 5m long, 50cm large, 10 cm thick inscribed with the words: Minh Mang the 17th, the year of Binh Than, commander Pham Huu Nhat of the naval force, ordered by the King to go to Hoang Sa to take care and make measurements for rememberance”.