Franco-Siamese Treaty of 1856

Treaty of Friendship, Commerce and Navigation, between Siam and France (French: Traité d'Amitié de Commerce et de Navigation, entre le Siam et le France, Thai: หนังสือสัญญาทางพระราชไมตรีประเทศสยามแลประเทศฝรั่งเศส) was a treaty between Second French Empire under Emperor Napoleon III and the Siamese Rattanakosin Kingdom under King Mongkut or King Rama IV of Siam, signed on 15 August 1856 as one of many unequal treaties that Siam concluded with Western nations during this period, opening the new stage of Franco–Siamese relations in the era of Western imperialism.

This Franco–Siamese Treaty of 1856 was based on the preceding Anglo–Siamese Bowring Treaty of April 1855, also based on the Sino–French Treaty of Whampoa (1844). This treaty was the result of early stages of French expansion into the Far East in competition with Great Britain, also the result of Siamese procurement of relations with France in order to counter-balance other Western powers, namely Britain. In 1855, Emperor Napoleon III of France appointed Charles de Montigny the French Consul at Shanghai as French imperial plenipotentiary to negotiate a new diplomatic and commercial treaty with Siam (now Thailand). This was the first Franco–Siamese official diplomatic engagement since the late seventeenth century during the reigns of King Louis XIV of France and King Narai of Ayutthaya. Montigny arrived in Bangkok, Siam's royal capital, in July 1856. King Mongkut appointed five Siamese plenipotentiaries to discuss the new treaty with Montigny, leading to the conclusion and signing of the treaty on August 15, 1856. This Franco–Siamese Montigny treaty contained twenty-four articles. The main terms of this treaty were;

• Establishment of French consular authority and French extraterritorial jurisdiction in Siam
• Siamese commercial concessions to France, including the low, fixed-rate import duty of three percent
• Siamese guarantee of freedom of Catholic Christian proselytization and Roman Catholic religion in Siam
• Right of residence and land ownership for French subjects in Siam, only in the area surrounding Bangkok

These treaty terms were almost identical to the Anglo–Siamese Bowring Treaty, concluded in April 1855 between Siam and Great Britain, also identical to the American–Siamese Harris Treaty, concluded in May 1856 between Siam and the United States. Clause on the matters concerning Catholic propagation of faith in Siam was unique to this Montigny Treaty, which also led to the Siamese diplomatic mission to France in 1861. Another important clause of this treaty was the unrestricted access of French warships to Bangkok, resulting in the French bringing warships to Bangkok to impose gunboat diplomacy on Siam in 1865 and 1893.

The Franco–Siamese Treaty of 1856 remained in effect for 68 years. French extraterritorial jurisdiction in Siam was partially curtailed by the Franco-Siamese treaty of 1907, in which Siam ceded Northwestern Cambodia including Battambang, Siemreap and Sisophon to French Indochina. In 1924, Francis Bowes Sayre, an American Harvard Law professor, acting as the representative of Siam, went on a European tour to negotiate new treaties with various European nations on behalf of Siam, leading to the conclusion of Franco–Siamese Treaty of 1925, which abolished most of the terms of the Franco–Siamese Treaty of 1856, including the low import duties and most of the French consular and extraterritorial jurisdiction in Siam.