Vietnamese works and documents proving the right of discovery and sovereignty of Vietnam over the Hoàng Sa (Paracels) and Trường Sa (Spratlys) archipelagoes date back to the 15th century; earlier documents may have been destroyed or lost during the period of domination by northern invaders or in incessant wars.
The oldest work that refers to the existence of the islands is Thiên Nam tứ chí lộ đồ thư (Route Map from the Capital to the Four Directions) (1630 – 1653) compiled by Đỗ Bá, alias Công Đạo. This document includes maps of Annam since the 15th century, some of which depict the Paracels and Spratlys archipelagoes in the East Sea under the names Bãi Cát Vàng and Trường Sa, belonging to Quảng Ngãi prefecture:
“In the middle of the sea is a long sand bank, called Bãi Cát Vàng (golden sand bank) with a length of 400 miles and a width of 20 miles, stretching in the middle of the sea from Đại Chiêm to Sa Vĩnh estuary. Foreign ships would be drifted and stranded on the bank if they traveled on the inner side of the sandbank under the southwest wind or on the outer side under the northeast wind; sailors would have starved to death and leave all their goods there.”
One of the maps in Phủ biên tạp lục (Miscellany on the Pacification at the Frontier) compiled by scholar Lê Quý Đôn in 1776 describes in detail the geographical conditions and natural resources in Hoàng Sa and Trường Sa, and the exploitation of the Nguyễn Lords on the two archipelagoes – (Source: Authorities of External Information, Ministry of Information and Communications)
Phủ biên tạp lục (1776) compiled by Lê Quý Đôn, the then deputy governor of Thuận Hóa region, reads:
“…Bình Sơn district of Quảng Ngãi prefecture includes the coastal commune of An Vĩnh, offshore to its northeast are many islands and approximately 130 mountains separated by sea waters, which can take from few hours to few days to go from one to another. Streams of fresh water can be found on these mountains. Within the islands is a 30-dặm long, flat and wide golden sand bank, on which the water is so transparent that one can see through.”
Đại Nam thực lục tiền biên (The First Part of The Chronicles of Đại Nam), the part writing about the Nguyễn Lords (1600-1775), Volume X, records the names of Hoàng Sa and Trường Sa and the management activities of the Vietnamese authorities:
“Offshore the An Vĩnh commune, Bình Sơn district, Quảng Ngãi prefecture, are more than 130 sand-banks, whose distance from one another can take anywhere from a few hours to a few days to travel, which are customarily called “Vạn Lý Hoàng Sa” with freshwater wells on the sand-banks. Sea products in the area include sea cucumbers, tortoise-shells, mollusks, sea turtles, and so on. In the early days of the Dynasty, Hoàng Sa detachment was established with 70 sailors selected from An Vĩnh commune, in the third month of every year, they sailed for about three days and three nights to the islands to collected goods there and returned in the eighth month. There was also another detachment named Bắc Hải, whose sailors were chosen from Tứ Chính ward in Bình Thuận or Cảnh Dương commune and ordered to sail boats to Bắc Hải and Côn Lôn areas to collect goods. This detachment was also under the command of the Hoàng Sa detachment.” 
Vietnamese map compiled by Đỗ Bá in the 17th century. The caption on the map indicating Quảng Ngãi prefecture clearly reads: “In the middle of the sea lies stretch of sand bank called Bãi Cát Vàng”, and “during the last month of every winter, the Nguyễns send eighteen boats there to collect goods…” – Photo: biengioilanhtho.gov.vn
Other official works compiled by Quốc Sử quán (the National History Institute) under the Nguyễn Dynasty, such as Đại Nam thực lục chính biên (1848), Khâm định Đại Nam hội diễn sử lệ (1843 – 1851), Đại Nam nhất thống chí (1865 – 1882), Lịch triều hiến chương loại chí (1821), Hoàng Việt địa dư chí (1833), and Việt sử cương giám khảo lược (1876) have similar description about Hoàng Sa and Trường Sa. Đại Nam thực lục chính biên đệ nhị kỷ, Volume 165, also affirms the assessment of the Ministry of Public Works submitted to the king in the Bính Thân year, the 17th year of the reign of Minh Mạng (1836, i.e. the 16th year of the reign of Daoguang under the Qing Dynasty): “Hoàng Sa is our territory in the sea, which is very important and difficult to access.” Đại Nam nhất thống chí, an unified collection of geography and history of Đại Nam, the part describing the torpography of Quảng Ngãi province, reads: “…to the east is Hoàng Sa Island in the open sea, serving as the protection dike…” All these are official sources with true value.
Viện Hán – Nôm Hà Nội (Hanoi Institute of Hán-Nôm Studies) still keeps tens of official documents of the Nguyễn Dynasty, which consist of reports of the Ministry of Public Works, the Ministry of Finance and other royal agencies, as well as edicts of the kings on activities to exercise Vietnam’s sovereignty over the archipelagoes.
A number of Vietnamese maps depicted the islands as part of Vietnam’s territory, particularly Đại Nam nhất thống toàn đồ (1838). Besides, other geography and history books such as Sử học bị khảo written by Đặng Xuân Bảng, Địa dư toát yếu (compiled under the reign of Duy Tân from 1907-1916), Quảng Thuận đạo sử tập, Trung kỳ địa dư lược, and Quảng Ngãi tỉnh chí, all contain paragraphs and maps confirming that Hoàng Sa belongs to Quảng Ngãi province. In family archives of the clans of Phạms and Đặngs who live on Lý Sơn Island, royal ordinances of Ming Mạng Emperor on assigning these families to select strong and good-at-swimming youths, to join the Hoàng Sa detachment, are still kept…
By Dr. Nguyễn Hồng Thao
 Đại Nam thực lục tiền biên, History Publishing House, Hanoi, 1962, Volume.1, page 22
“Phát hiện tài liệu quý liên quan đến quần đảo Hoàng Sa” (The discovery of precious documents related to the Hoàng Sa archipelago), Lao Động Newspaper, Issue No. 71, April 1st 2009.