Gia Long Emperor Gia Long ( 8 February 1762 – 3 February 1820 ) , born Nguyễn Phúc Ánh , often referred to simply as Nguyễn Ánh ) , was the first Emperor of the Nguyễn Dynasty of Vietnam . Unifying what is now modern Vietnam in 1802 , he founded the Nguyễn Dynasty , the last of the Vietnamese dynasties . A nephew of the last Nguyễn lord who ruled over southern Vietnam , Nguyễn Ánh was forced into hiding in 1777 as a fifteen - year - old when his family was slain in the Tây Sơn revolt . After several changes of fortune in which his loyalists regained and again lost Saigon , he befriended the French Catholic priest Pigneau de Behaine . Pigneau championed his cause to the French government — and managed to recruit volunteers when this fell through — to help Nguyễn Ánh regain the throne . From 1789 , Nguyễn Ánh was once again in the ascendancy and began his northward march to defeat the Tây Sơn , eventually moving by 1802 to the border with China , which had previously been under the control of the Trịnh lords . When this was over , he had reunited Vietnam after centuries of internecine feudal warfare with a greater land mass than ever before , stretching from China down to the Gulf of Siam . Gia Long ' s rule was noted for its Confucian orthodoxy . He repealed Tây Sơn reforms and reinstated the classical Confucian education and civil service system . He moved the capital from Hanoi south to Huế as the country ' s populace had also shifted south over the preceding centuries , and built up fortresses and a palace in his new capital . Using French expertise , he modernized Vietnam ' s defensive capabilities . In deference to the assistance of his French friends , he tolerated the activities of Roman Catholic missionaries , something that became increasingly restricted under his successors . Under his rule , Vietnam strengthened its military dominance in Indochina , expelling Siamese forces from Cambodia and turning it into a vassal state . Early years . Born on 8 February 1762 , Nguyễn Ánh was the son of Nguyễn Phúc Luân and Nguyen Thi Hoan . Luan was the designated heir of Lord Nguyễn Phúc Khoát of southern Vietnam . However , a high - ranking mandarin named Trương Phúc Loan changed Khoat ' s will of succession on his deathbed , and installed Luan ' s younger brother Nguyễn Phúc Thuần on the throne in 1765 . Luan was jailed and died in the same year . However , Thuan lost his position as lord of southern Vietnam and was killed during the Tây Sơn rebellion led by the brothers Nguyễn Nhạc , Nguyễn Huệ and Nguyễn Lữ in 1777 . Nguyễn Ánh was the most senior member of the ruling family to have survived the Tây Sơn victory , which pushed the Nguyễn from their heartland in central Vietnam , southwards towards Saigon and into the Mekong Delta region in the far south . Nguyễn Ánh fled to Ha Tien on the southern coastal tip of Vietnam , where he met Pigneau de Behaine , a French priest who became his adviser and played a major part in his rise to power . Together , they escaped to the island of Pulo Panjang in the Gulf of Siam . Pigneau hoped that by playing a substantial role in a Nguyễn Ánh victory , he would be in position to lever important concessions for the Catholic Church in Vietnam , helping its expansion in South East Asia . In late 1777 , the main part of the Tây Sơn army left Saigon to go north and attack the Trịnh lords , who ruled the other half of Vietnam . Nguyễn Ánh stealthily returned to the mainland , rejoining his supporters and reclaimed the city . He was crucially aided by the efforts of Do Thanh Nhon , who had organized an army for him , which was supplemented by Cambodian mercenaries and Chinese pirates . The following year , Nhon expelled further Tây Sơn troops from the surrounding province of Gia Dinh , and inflicted heavy losses on the Tây Sơn naval fleet . Taking advantage of the more favorable situation , Nguyễn Ánh sent a diplomatic mission to Siam to propose a treaty of friendship . However , this pact was derailed in 1779 when the Cambodians held an uprising against their pro - Siamese leader Ang Non . Nguyễn Ánh sent Nhon to help the uprising , which saw Ang Non defeated decisively and executed . Nhon returned to Saigon with high honor and concentrated his efforts on improving the Nguyễn navy . In 1780 , in an attempt to strengthen his political status , Nguyễn Ánh proclaimed himself Nguyễn vương ( " Nguyễn king " or " Nguyễn ruler " in Vietnamese ) . Then , in 1781 , Nguyễn Ánh sent further forces to prop up the Cambodian regime against Siamese armies who wanted to reassert their control . Shortly thereafter , Nguyễn Ánh had Nhon brutally murdered . The reason remains unclear , but it was postulated that he did so because Nhon ' s fame and military success was overshadowing him . The Tây Sơn brothers reportedly broke out in celebration upon hearing of Nhon ' s execution , as Nhon was the Nguyễn officer that they feared the most . Nhon ' s supporters rebelled , weakening the Nguyễn army , and within a few months , the Tây Sơn had recaptured Saigon mainly on the back of naval barrages . Nguyễn Ánh was forced to flee to Ha Tien , and then onto the island of Phu Quoc . Meanwhile , some of his forces continued to resist in his absence . In October 1782 , the tide shifted again , when forces led by Nguyễn Phúc Mân , Nguyễn Ánh ' s younger brother , and Chau Van Tiep drove the Tây Sơn out of Saigon . Nguyễn Ánh returned to Saigon , as did Pigneau The hold was tenuous , and a counterattack by the Tây Sơn in early 1783 saw a heavy defeat to the Nguyễn , with Nguyen Man killed in battle . Nguyễn Ánh again fled to Phu Quoc , but this time his hiding place was discovered . He managed to escape the pursuing Tây Sơn fleet to Koh - rong island in the Bay of Kompongsom . Again , his hideout was discovered and encircled by the rebel fleet . However , a typhoon hit the area , and he managed to break the naval siege and escape to another island amid the confusion . In early - 1784 , Nguyễn Ánh went to seek Siamese aid , which was forthcoming , but the extra 20 , 000 men failed to weaken the Tây Sơn ' s hold on power . This forced Nguyễn Ánh to become a refugee in Siam in 1785 . To make matters worse , the Tây Sơn regularly raided the rice growing areas of the south during the harvesting season , depriving the Nguyễn of their food supply . Nguyễn Ánh eventually came to the conclusion that using Siamese military aid would generate a backlash amongst the populace , due to prevailing Vietnamese hostility towards Siam . Pigneau and French assistance . Deflated by his situation , Nguyễn Ánh asked Pigneau to appeal for French aid , and allowed Pigneau to take his son Nguyễn Phúc Cảnh with him as a sign of good faith . This came about after Nguyễn Ánh had considered enlisting English , Dutch , Portuguese and Spanish assistance . Pigneau advised against Nguyễn Ánh ' s original plan to seek Dutch aid from Batavia , fearing that the support of the Protestant Dutch would hinder the advancement of Catholicism . Pigneau left Vietnam in December , arriving in Pondicherry , India in February 1785 with Nguyễn Ánh ' s royal seal . Nguyễn Ánh had authorized him to make concessions to France in return for military assistance . The French administration in Pondicherry , led by acting governor Coutenceau des Algrains , was conservative in outlook and resolutely opposed intervention in southern Vietnam . To compound the already complex situation , Pigneau was denounced by Spanish Franciscans in the Vatican , and he sought to transfer his political mandate to Portuguese forces . The Portuguese had earlier offered Nguyễn Ánh 56 ships to use against the Tây Sơn . In July 1786 , after more than 12 months of fruitless lobbying in Pondicherry , Governor de Cossigny allowed Pigneau to travel back to France to directly ask the royal court for assistance . Arriving at the court of Louis XVI in Versailles in February 1787 , Pigneau had difficulty in gathering support for a French expedition in support of Nguyễn Ánh . This was due to the parlous financial state of the country prior to the French Revolution . Pigneau was helped by Pierre Poivre , who had previously been involved in seeking French commercial interests in Vietnam . Pigneau told the court that if France invested in Nguyễn Ánh and acquired a few fortified positions on the Vietnamese coast in return , then they would have the capability to " dominate the seas of China and of the archipelago " , and with it , control of Asian commerce . In November 1787 , a treaty of alliance was concluded between France and Cochinchina — the European term for southern Vietnam — in Nguyễn Ánh ' s name . Pigneau signed the treaty as the " Royal Commissioner of France for Cochinchina " . France promised four frigates , 1 , 650 fully equipped French soldiers and 250 Indian sepoy s in return for the cession of Pulo Condore and Tourane ( Da Nang ) , as well as tree trade to the exclusion of all other countries . However , the freedom to spread Christianity was not included . However , Pigneau found that Governor Thomas Conway of Pondicherry was unwilling to fulfill the agreement ; Conway had been instructed by Paris to determine when to organize the aid , if at all . Pigneau was thus forced to use funds raised in France to enlist French volunteers and mercenaries . He also managed to procure several shipments of arms and munitions from Mauritius and Pondicherry . Meanwhile , Nguyễn Ánh had stayed in Siam with a contingent of troops until August 1787 . His soldiers served in Siam ' s war against Bodawpaya of Burma . Having consolidated their hold on southern Vietnam , the Tây Sơn decided to move north to unify the country . However , the withdrawal of troops from the Gia Dinh garrison weakened them their hold on the south . This was compounded by reports that Nguyễn Nhạc was being attacked near Qui Nhơn by his own brother Nguyễn Huệ , and that more Tây Sơn troops were being evacuated from Gia Dinh by their commander Dang Van Tran in order to aid Nguyễn Nhạc . Sensing Tây Sơn vulnerability in the south , Nguyễn Ánh assembled his forces at home and abroad in preparation for an immediate offensive . Nguyễn Ánh secretly left Siam and headed for southern Vietnam , but he failed in his first attempt to recapture Gia Dinh . He eventually succeeded in taking Mỹ Tho , made it the main staging point for his operations , and rebuilt his army . After a hard - fought battle , his soldiers captured Saigon on 7 September 1788 . Eventually , Pigneau assembled four vessels to sail to Vietnam from Pondicherry , arriving in Saigon on 24 July 1789 . The combined forces helped to consolidate Nguyễn Ánh ' s hold on southern Vietnam . The exact magnitude of foreign aid and the importance of their contribution to Gia Long ' s success is a point of dispute . Earlier scholars asserted that up to 400 Frenchmen enlisted , but more recent work has claimed that less than 100 soldiers were present , along with approximately a dozen officers . Consolidation of southern Vietnam . The French officers enlisted by Pigneau helped to train Nguyễn Ánh ' s armed forces and introduced Western technological expertise to the war effort . The navy was trained by Jean - Marie Dayot , who supervised the construction of bronze - plated naval vessels . Olivier de Puymanel was responsible for training the army and the construction of fortifications . He taught the troops various methods of manufacturing and using European - style artillery and introduced European infantry formations and tactics . Pigneau and other missionaries acted as business agents for Nguyễn Ánh , purchasing munitions and other military supplies . Pigneau also served as an advisor and de facto foreign minister until his death in 1799 . Upon Pigneau ' s death , Gia Long ' s funeral oration described the Frenchman as " the most illustrious foreigner ever to appear at the court of Cochinchina " . Pigneau was buried in the presence of the crown prince , all mandarins of the court , the royal bodyguard of 12 , 000 men and 40 , 000 mourners . Fortifications . Following the recapture of Saigon , Nguyễn Ánh consolidated his power base and prepared the destruction of the Tây Sơn . His enemies had regularly raided the south and confiscated the annual rice harvests , so Nguyễn Ánh was keen to strengthen his defense . One of Nguyễn Ánh ' s first actions was to ask the French officers to design and supervise the construction of a modern European - style citadel in Saigon . The citadel was designed by Theodore Lebrun and de Puymanel , with 30 , 000 people mobilized for its construction in 1790 . The townfolk and their mandarins were punitively taxed for the work , the laborers were worked so hard that they revolted . When finished , the stone citadel had a perimeter measuring 4 , 176 meters in a Vauban model . The fortress was bordered on three sides by pre - existing waterways , bolstering its natural defensive capability . Following the construction of the citadel , the Tây Sơn never again attempted to sail down the Saigon River and try to recapture the city — its presence having endowed Nguyễn Ánh with a substantial psychological advantage over his opponents . Nguyễn Ánh took a keen personal interest in fortifications , ordering his French advisors to travel home and bring back books with the latest scientific and technical studies on the subject . Agrarian reform and economic growth . With the southern region secured , Nguyễn Ánh turned his attention to agrarian reforms . Due to Tây Sơn naval raids on the rice crop via inland waterways , the area suffered chronic rice shortages . Although the land was extremely fertile , the region was agriculturally underexploited , having been occupied by Vietnamese settlers only relatively recently . Furthermore , agricultural activities had also been significantly curtailed during the extended warfare with the Tây Sơn . Nguyễn Ánh ' s agricultural reforms were based around extending to the south a traditional form of agrarian expansion , the " đồn điền " , which roughly translates as " military settlement " or " military holding " , the emphasis being on the military origin of this form of colonization . These were first used during the 15th century reign of Lê Thánh Tông in the southward expansion of Vietnam . The central government supplied military units with agricultural tools and grain for nourishment and planting . The soldiers were then assigned land to defend , clear and cultivate , and had to pay some of their harvest as tax . In the past , a military presence was required because the land was being seized from the conquered indigenous population . Under Nguyễn Ánh ' s rule , pacification was not usually needed but the basic model remained intact . Settlers were granted fallow land , given agricultural equipment , work animals and grain . After several years , they were required to pay grain tax . The program greatly reduced the amount of idle , uncultivated land . Large surpluses of grain , taxable by the state , resulted . By 1800 , the increased agricultural productivity had allowed Nguyễn Ánh to support a sizeable army of more than 30 , 000 soldiers and a navy of more than 1 , 200 vessels . The surplus from the state granary was sold to European and Asian traders to facilitate the importation of raw materials for military purposes , in particular iron , bronze , and sulfur . The government also purchased castor sugar from local farmers and traded it for weapons from European manufacturers . The food surplus allowed Nguyễn Ánh to engage in welfare initiatives that improved morale and loyalty among his subjects , thereby increasing his support base . The surplus grain was deposited in granaries built along the northward route out of Saigon , following the advance of the Nguyễn army into Tây Sơn territory . This allowed his troops to be fed from southern supplies , rather than eating from the areas that he was attempting to conquer or win over . Newly acquired regions were given tax exemptions , and surrendered Tây Sơn mandarins were appointed to equivalent positions with the same salaries in the Nguyễn administration . Naval buildup . Nguyễn Ánh used his new base to improve his inferior navy , which was much smaller than the Tây Sơn fleet and hitherto unable to prevent their rice raids . Nguyễn Ánh had first attempted to acquire modern naval vessels in 1781 , when on the advice of Pigneau , he had chartered Portuguese vessels of European design , complete with crew and artillery . This initial experience proved to be disastrous . For reasons that remain unclear , two of the vessels fled in the midst of battle against the Tây Sơn , while angry Vietnamese soldiers killed the third crew . In 1789 , Pigneau returned to Vietnam from Pondicherry with two vessels , which stayed in the Nguyễn service long - term . Over time , Vietnamese sailors replaced the original French and Indian crew under the command of French officers . These vessels became the foundation for an expanded military and merchant Nguyen naval force , with Nguyễn Ánh chartering and purchasing more European vessels to reinforce Vietnamese - built ships . However , traditional Vietnamese - style galleys and small sailing ships remained the majority of the fleet . By 1794 , two European vessels were operating together with 200 Vietnamese boats against the Tây Sơn near Qui Nhơn . In 1799 , a British trader by the name of Berry reported that the Nguyễn fleet had departed Saigon along the Saigon River with 100 galleys , 40 junks , 200 smaller boats and 800 carriers , accompanied by three European sloops . In 1801 , one naval division was reported to have included nine European vessels armed with 60 guns , five vessels with 50 guns , 40 with 16 guns , 100 junks , 119 galleys and 365 smaller boats . Most of the European - style vessels were built in the shipyard that Nguyễn Ánh had commissioned in Saigon . He took a deep personal interest in the naval program , directly supervising the work and spending several hours a day dockside . One witness noted " One principal tendency of his ambition is to naval science , as a proof of this he has been heard to say he would build ships of the line on the European plan . " By 1792 , fifteen frigates were under construction , with a design that mixed Chinese and European specifications , equipped with 14 guns . The Vietnamese learned European naval architecture by dismantling an old European vessel into its components , so that Vietnamese shipbuilders could understand the separate facets of European shipbuilding , before reassembling it . They then applied their newfound knowledge to create replicas of the boats . Nguyễn Ánh studied naval carpentry techniques and was said to be adept at it , and learned navigational theory from the French books that Pigneau translated , particularly Denis Diderot and Jean le Rond d ' Alembert ' s " Encyclopédie " . The Saigon shipyard was widely praised by European travelers . Despite his extensive reliance on French officers on matters of military technology , Nguyễn Ánh limited his inner military circle to Vietnamese . The Frenchmen decried his refusal to take their tactical advice . Chaigneau reported that the Europeans continually urged Nguyễn Ánh to take the initiative and launch bold attacks against Tây Sơn installations . Nguyễn Ánh refused , preferring to proceed slowly , consolidating his gains in one area and strengthening his economic and military base , before attacking another . Over time , Nguyễn Ánh gradually reduced the military role of his French allies on the battlefield . In the naval battle at Thi Nai in 1792 , Dayot led the Nguyễn naval attack , but by 1801 , a seaborne offensive in the same area was led by the Nguyen Van Truong , Vo Duy Nguy and Lê Văn Duyệt , with Chaigneau , Vannier , and de Forsans in supporting positions . The infantry attack on Qui Nhơn in 1793 was conducted , according to Nguyen historiography , in cooperation with " Western soldiers " . The same source recorded that by 1801 , Nguyen operations in the same area were directed by Vietnamese generals , whereas Chaigneau and Vannier were responsible for organizing supply lines . Unification of Vietnam . In 1792 , the middle and the most notable of the three Tây Sơn brothers , Nguyễn Huệ Quang Trung , who had gained recognition as Emperor of Vietnam by driving the Lê Dynasty and China out of northern Vietnam , died suddenly . Nguyễn Ánh took advantage of the situation and attacked northwards . By now , the majority of the original French soldiers , whose number peaked at less than 80 by some estimates , had departed . The majority of the fighting occurred in and around the coastal towns of Nha Trang in central Vietnam and Qui Nhơn further to the south in Bình Định Province , the birthplace and stronghold of the Tây Sơn . Nguyễn Ánh began by deploying his expanded and modernised naval fleet in raids against coastal Tây Sơn territory . His fleet left Saigon and sailed northward on an annual basis during June and July , carried by southwesterly winds . The naval offensives were reinforced by infantry campaigns . His fleet would then return south when the monsoon ended , on the back of northeasterly winds . The large European wind - powered vessels gave the Nguyễn navy a commanding artillery advantage , as they has a superior range to the Tây Sơn cannons on the coast . Combined with traditional galleys and a crew that was highly regarded for its discipline , skill and bravery , the European - style vessels in the Nguyễn fleet inflicted hundreds of losses against the Tây Sơn in 1792 and 1793 . In 1794 , after a successful campaign in the Nha Trang region , Nguyễn Ánh ordered de Puymanel to build a citadel at Duyen Khanh , near the city , instead of retreating south with the seasonal northeasterly breeze . A Nguyen garrison was established there under the command of Nguyễn Ánh ' s eldest son and heir , Nguyễn Phúc Cảnh , assisted by Pigneau and de Puymanel . The Tây Sơn laid siege to Duyen Khanh in May 1794 , but Nguyen forces were able to keep them out . Shortly after the siege ended , reinforcements arrived from Saigon and offensive operations against the Tây Sơn duly resumed . The campaign was the first time that the Nguyễn were able to operate in Tây Sơn heartland during an unfavorable season . The defensive success of the citadel was a powerful psychological victory for the Nguyễn , demonstrating their ability to penetrate Tây Sơn territory at all times of year . The Nguyễn then proceeded to slowly erode the Tây Sơn heartland . Heavy fighting occurred at the fortress of Qui Nhơn , until it was captured in 1799 by Nguyen Canh ' s forces . However , the city was quickly lost and was not regained until 1801 . The superior firepower of the improved navy played the decisive role in the ultimate recapture of the city , supporting a large overland attack . After the capture of their stronghold at Qui Nhơn , the Tây Sơn , led by Quang Trung ' s son Quang Toan , came quickly . In June , the central city of Huế — the former capital of the Nguyễn — fell and Nguyễn Ánh crowned himself emperor , under the reign name Gia Long , which was derived from " Gia Định " ( Saigon ) and " Thăng Long " ( Hanoi ) to symbolize the unification of north and south Vietnam . He then quickly overran the north , with Hanoi captured on 22 July 1802 . After a quarter - century of continuous fighting , Gia Long had unified what is now modern Vietnam , and elevated his family to a position never previously occupied by Vietnamese royalty . Vietnam had never before occupied a larger landmass . Gia Long became the first Vietnamese ruler to reign over territory stretching from China in the north , all the way to the Gulf of Siam and the Cà Mau peninsula in the south . Gia Long ' s then petitioned the Qing Dynasty of China for official recognition , which was promptly granted . The French failure to honour the treaty signed by Pigneau meant Vietnam was not bound to cede the territory and trading rights that they had promised . Rule . Gia Long ' s rule was noted for its strict Confucian orthodoxy . Upon toppling the Tây Sơn , he repealed their reforms and reimposed a classical Confucian education and civil service system . He moved the capital from Hanoi in the north to Huế in central Vietnam to reflect the southward migration of the population over the preceding centuries . The emperor built new fortresses and a palace in his new capital . Using French expertise , Gia Long modernised Vietnam ' s defensive capabilities . In deference to the assistance of his French friends , he tolerated the activities of Catholic missionaries , something that was increasingly restricted by his successors . Under Gia Long ' s rule , Vietnam strengthened its military dominance in Indochina , expelling Siam from Cambodia and turning it into a vassal . Despite this , he was relatively isolationist in outlook towards European powers . Administrative structure . During the war era , Nguyễn Ánh had maintained an embryonic bureaucracy in an attempt to prove his leadership ability to the people . Due to the incessant warfare , military officers were generally the most prominent members of his inner circle . This dependency on military backing continued to manifest itself throughout his reign . Vietnam was divided into three administrative regions . The old patrimony of the Nguyễn formed the central part of the empire ( " vùng Kinh Kỳ " ) , with nine provinces , five of which were directly ruled by Gia Long and his mandarins from Huế . The central administration at Huế was divided into six ministries : Public affairs , finance , rites , war , justice and public works . Each was under a minister , assisted by two deputies and two or three councillors . Each of these ministries had around 70 employees assigned to various units . The heads of these ministries formed the Supreme Council . A treasurer general and a Chief of the Judicial Service assisted a governor general , who was in charge of a number of provinces . The provinces were classified into " trấn " and " dinh " . These were in turn divided into " phủ " , " huyện " and " châu " . All important matters were examined by the Supreme Council in the presence of Gia Long . The officials tabled their reports for discussion and decision - making . The bureaucrats involved in the Supreme Council were selected from the high - ranking mandarins of the six ministries and the academies . Gia Long handled the northern and southern regions of Vietnam cautiously , not wanting them to be jarred by rapid centralization after centuries of national division . Tonkin , with the administrative seat of its imperial military protector ( " quan tổng trấn " ) at Hanoi had thirteen provinces ( " tổng trấn Bắc Thành " ) , and in the Red River Delta , the old officials of the Le administration continued in office . In the south , Saigon was the capital of the four provinces of Cochinchina ( " tổng trấn Nam Hà " ) , as well as the seat of the military protector . The citadels in the respective cities directly administered their military defense zones . This system allowed Gia Long to reward his leading supporters with highly powerful positions , giving them almost total autonomy in ordinary administrative and legal matters . This system persisted until 1831 – 32 , when his son Minh Mạng centralized the national government . In his attempts to re - establish a stable administration after centuries of civil war , Gia Long was not regarded as being innovative , preferring the traditional administration framework . When Gia Long unified the country , it was described as Charles Maybon as being chaotic : " The wheels of administration were warped or no longer existed ; the cadres of officials were empty , the hierarchy destroyed ; taxes were not being collected , lists of communal property had disappeared , proprietary titles were lost , fields abandoned ; roads bridges and public granaries had not been maintained ; work in the mines had ceased . The administration of justice had been interrupted , every province was a prey to pirates , and violation of law went unpunished , while even the law itself had become uncertain . " Foreign military relations . During the 17th and 18th centuries , the Cambodia ' s empire had been in decline as Vietnamese people migrated south into the Mekong Delta , which was hitherto Khmer territory . Furthermore , Cambodia had been periodically invaded by both Vietnam and Siam . Cambodia lurched uneasily between both poles of domination as dictated by the internal strife of her two larger neighbors . In 1796 , Ang Eng , a pro - Siamese king had died , leaving Ang Chan , who was born in 1791 . When Gia Long unified Vietnam , Eng was given investiture by Siam in order to hold out Vietnamese influence , but in 1803 , a Cambodian mission paid tribute to Vietnam in attempt to placate Gia Long , something that became an annual routine . In 1807 , Ang Chan requested formal investiture as a vassal of Gia Long . Gia Long responded by sending an ambassador bearing the book of investiture , together with a seal of gilded silver . In 1812 , Ang Chan refused a request from his brother Ang Snguon to share power , leading to a rebellion . Siam sent troops to support the rebel prince , hoping to enthrone him and wrest influence from Gia Long over Cambodia . In 1813 , Gia Long responded by sending a large military contingent that forced the Siamese and Ang Snguon out of Cambodia . As a result , a Vietnamese garrison was permanently installed in the citadel at Phnom Penh , the Cambodian capital . Thereafter , Siam made no attempts to regain control of Cambodia during Gia Long ' s rule . Napoleon ' s aims to conquer Vietnam as a base to challenge British supremacy in India never materialized , having been occupied by vast military ambitions on mainland Europe . However , France remained the only European power with permanent spokesmen in Vietnam during his reign . Trade relations . Pigneau ' s aborted deal with France allowed Gia Long to keep his country closed to western trade . Gia Long was generally dismissive of European commercial overtures . This was part of a policy of trying to maintain friendly relations with every European power by granting favors to none . In 1804 , a British delegation attempted to negotiate trading privileges with Vietnam . It was the only offer of its kind until 1822 , such was the extent of European disinterest in Asia during the Napoleonic Wars . Gia Long had purchased arms from British firms in Madras and Calcutta on credit , prompting the British East India Company to send John Roberts to Huế . However , Roberts ' s gifts were turned away and the negotiations for a commercial deal never started . The United Kingdom then made a request for the exclusive right to trade with Vietnam and the cession of the island of Cham near Faifo , which was rejected , as were further approaches from the Netherlands . Both of these failed attempts were attributed to the influence of the French mandarins . In 1817 , the French Prime Minister Armand - Emmanuel du Plessis dispatched the " Cybele " , a frigate with 52 guns to Tourane ( now Da Nang ) to " show French sympathy and to assure Gia Long of the benevolence of the King of France " . The captain of the vessel was turned away , ostensibly on grounds of protocol for not carrying a royal letter from the French king . Gia Long kept four French officers in his service after his coronation : Philippe Vannier , Jean - Baptiste Chaigneau , de Forsans and the doctor Despiau . All became high ranking mandarins and were treated well . They were given 50 bodyguards each , ornate residences and were exempt for having to prostrate before the emperor . Recommendations from French officials in Pondicherry to Napoleon Bonaparte suggesting the re - establishment of diplomatic relations with Vietnam were fruitless due to the preoccupation with war in Europe . However , French merchants from Bordeaux were later able to begin trading with Vietnam after the further efforts of the Duc de Richelieu . Domestic policies and capital works . Gia Long abolished all large landholding by princes , nobles and high officials . He dismantled the 800 - year old practice of paying officials and rewarding or endowing nobles with a portion of the taxes from a village or a group thereof . Existing highways were repaired and new ones constructed , with the north - south road from Saigon to Lạng Sơn put under restoration . He organised a postal service to operate along the highways and public storehouses were built to alleviate starvation in drought - affected years . Gia Long enacted monetary reform and implemented a more socialized agrarian policy . However , the population growth far outstripped that of land clearing and cultivation . There was little emphasis on innovation in agricultural technology , so the improvements in productivity were mainly derived from increasing the amount of cultivated farmland . Although the civil war was over , Gia Long decided to add to the two citadels that had been built under the supervision of French officers . Gia Long was convinced of their effectiveness and during his 18 - year reign , a further 11 citadels were built throughout the country . The majority were built in the Vauban style , with pentagonal or hexagonal geometry , while a minority , including the one in Huế , were built in a four - sided traditional Chinese design . The fortresses were built at Vinh , Thanh Hóa , Bắc Ninh , Hà Tĩnh , Thái Nguyên and Hải Dương in the north , Huế , Quảng Ngãi , Khánh Hòa and Bình Định in the centre , and Vĩnh Long in the Mekong Delta . Construction was at its most intense in the early phase of Gia Long ' s reign — only one of the 11 were built in the last six years of his rule . De Puymanel and Lebrun left Vietnam before the end of the war , so the forts were designed by Vietnamese engineers who oversaw the construction . The position of Citadel Supervision Officer was created under the Ministry of War and made responsible for the work , underlining the importance that Gia Long placed on fortifications . Gia Long ' s fortifications program was marred by accusations that the people labored all day and part of the night in all weather conditions , and that as a direct consequence , land went fallow . Complaints of mandarin corruption and oppressive taxation were often levelled at his government . Following his coronation , Gia Long drastically reduced his naval fleet and by the 1810s , only two of the European - style vessels were still in service . The downsizing of the navy was mainly attributed to budgetary constraints caused by heavy spending on fortifications and transport infrastructure such as roads , dykes and canals . However , in 1819 , a new phase of shipbuilding was launched , with Gia Long personally supervising the dockyards . Social policy . In order to train and recruit government officials , Gia Long revived the Confucian court examinations that had been abolished by the Tây Sơn . In 1803 , he founded the National Academy ( " Quốc Tử Giám " ) at Huế . Its objective was to educate the sons of mandarins and meritorious students in the Confucian classical literature . In 1804 , Gia Long promulgated edicts establishing similar schools in the provinces , and guidelines to regulate their staff and curriculum . He appointed Directors of Education ( " quan đốc học " ) to oversee the provincial education system and the selection process for the entrance examinations into the National Academy , beginning in 1802 . The directors were assisted by Subordinate and Assistant Directors ( phó đốc học " or " trợ - giáo ) . Gia Long explained to his court in 1814 that the goal was to create a cadre of classically educated , politically loyal administrators : In 1807 , Gia Long opened the first civil service examinations held under the Nguyễn Dynasty , staged at regional level . From then on , the training and selection process for the imperial bureaucracy was largely centered on examinations . The curriculum for the examinations consisted of the " five classics and the four books " , which focused on Chinese history leading up to the Song Dynasty , while regarding other knowledge as irrelevant . Gia Long promulgated a new legal code to replace the system that had existed since the Hong Duc era of Lê Thánh Tông in the 15th century . Work started in 1811 under a group of scholars led by Nguyen Van Thanh , and in 1815 , the " Bộ luật Gia Long " ( " Gia Long Code " ) was issued . Although Gia Long claimed that his new system was a mixture of the Le code and Qing Dynasty system of China , most scholars regard it as being a near complete copy of the Qing code . The code was later translated into French by Paul - Louis - Félix Philastre . It focused on strengthening the power and authority of the emperor , his mandarins , and the traditional family unit . In cases of serious crimes , particularly those against the state , collective punishment was meted out to the family of the convict , including the death penalty . Now that Vietnam was unified , the center of gravity of the country was further to the south following centuries of southerly migration and conquest , so Gia Long moved the seat of government from Hanoi to Huế . Gia Long rebuilt the old citadel of Phú Xuân into a fortress stronghold . The structure was a square shape of 2 . 5 km per side . A 9 m rampart was cased with masonry and protected by protruding bastions , each defended by 36 guns . The exterior and interior were flanked and reinforced by a series of moats . The citadel ' s defenders included an 800 - strong elephant troop . The new palace structure , protocol and court dress were all taken directly from Qing Dynasty styles , and his palace and fortress was intended to be a smaller copy of the Chinese Forbidden City in the 1800s . Gia Long tolerated the Catholic faith of his French allies and permitted unimpeded missionary activities out of respect to his benefactors . The missionary activity was dominated by the Spanish in Tonkin and French in the central and southern regions . At the time of his death , there were six European bishops in Vietnam . The population of Christians was estimated at 300 , 000 in Tonkin and 60 , 000 in Cochinchina . However , he expressed dismay at the Catholic condemnation of the traditional ancestral worship , a basic tenet of Vietnamese culture . Gia Long was also known for his disdain for Buddhism , the religion practiced by the majority of the population . Despite its popularity among ladies of the court , Gia Long often restricted the activities of Buddhists . In August 1802 , Gia Long retaliated against the captured Tây Sơn leadership who had executed his family in the 1770s . The surviving members of the family and its leading generals and their families were executed . The remains of Quang Trung and his queen were exhumed and desecrated , and his son , the last Tây Sơn monarch Quang Toan was bound to four elephants and torn apart . Gia Long repealed the changes enacted by Quang Trung and reverted to the prior Confucian orthodoxy . This included restoring the civil service to the forefront of decision making , ahead of the army , and reversed Quang Trung ' s education reforms , which put science before the study of Confucian literature . Family and succession . Gia Long had three wives . In 1780 , during the war against the Tây Sơn , he married Tống Thị Lan , the daughter of a Nguyen general . She bore him two sons , the first being Crown Prince Nguyen Canh , and later Nguyen Phuc Chieu , who died shortly after birth . Following Gia Long ' s ascension to the throne , she became Empress Thừa Thiên . Sometime during the war with the Tây Sơn , he married his second wife Trần Thị Đang , a daughter of one of his ministers . She bore him three sons , Nguyễn Phúc Đảm , Nguyen Phuc Dai and Nguyen Phuc Chan , and was posthumously given the title of Empress Thuận Thiên . After his conquest of Vietnam , Gia Long , took his third wife , Le Ngoc Binh . A daughter of Lê Hiến Tông , the second - last emperor of the Lê Dynasty , she was betrothed by Emperor Quang Trung to his son Quang Toan . After Gia Long defeated the Tây Sơn and executed Quang Toan , he took her as his wife . Binh bore him two princes , Nguyen Phuc Quan and Nguyen Phuc Cu , and princesses An Nghia Ngoc Ngon and My Khue Ngoc Khue . Gia Long had almost 100 concubines who were daughters of his mandarins ; Gia Long did not favour polygamy but he did so to secure the loyalty of his inner circle . As Crown Prince Nguyen Canh had died of smallpox during the war against the Tây Sơn , it was assumed that Canh ' s son would succeed Gia Long as emperor , but in 1816 Nguyễn Phúc Đảm , the son of his second wife , was appointed instead , and ruled as Minh Mạng . Gia Long chose him for his strong character and his deep aversion to westerners , whereas Canh ' s lineage had converted to Catholicism and were reluctant to maintain their Confucian traditions such as ancestor worship . Before his ascension , Nguyễn Phúc Đảm was reported to have praised the Japanese for having expelled and eradicated Christianity from their country . Gia Long told his son to treat the Europeans respectfully , especially the French , but not to grant them any position of preponderance . Gia Long died on 3 February 1820 and was buried at the Thien Tho Tomb and posthumously named Thế Tổ Cao Hoàng đế .