Gialong (1802–20) owed his throne and the establishment of the Empire of Annam to the assistance of the French, particularly that of the missionary, Pierre Pigneau de Béhaine, Bishop of Adran. At this time the French undoubtedly could have had a protectorate over Annam for the asking, Gialong protected the French and Spanish missionaries during his reign and tried to give the French some trade advantages; but his successors, Ming Mang (1820–41), Thieu-Tri (1841–47), and Tuduc (1847–83), persecuted the missionaries and closed the country to European trade. In 1856, Charles de Montigny, a French diplomat, returning to his post in China, was ordered to make treaties of commerce with Siam and Annam and to secure the protection of the French missionaries in Annam. At Singapore, he received orders to stop at Cambodia, in response to overtures which Ang Duong, king of that country (1842–59), had made. toward a French protectorate. In 1856 Montigny made a treaty with Mong kut, king of Siam (1851–68), and although he stopped at the Cambodian seaport of Kampot, he did not visit the capital or make an alliance with Ang Duong, much to that monarch's chagrin. He was badly received at Tourane and Hué and did not succeed in making a treaty of any kind with Annam.