According to Wikipedia, the Treaty of Amity and Commerce between Siam and the United States (or Roberts Treaty of 1833) was written in Thai and English, together with translations in Portuguese and Chinese annexed to it. Why was it felt the need of annexing a Portuguese translation to it?

  • 2
    There are two possibilities: (a) to show Portugal (or China) what the treaty said or (b) the Americans and Thais spoke better Portuguese (or Chinese) than they spoke each other's language, and this was the drafting language of the treaty. My guess would be (b) for Portuguese, and (a) for Chinese
    – Henry
    Oct 20, 2017 at 8:22
  • @Henry My bet is also (b) for the Portuguese translation, but I would like to be sure about that. Oct 20, 2017 at 8:23
  • 3
    @JoséCarlosSantos - You don't have to bet. The answer is 'b', as explained by Ruschenberger, one of the participants of the Treaty. The other participant, Roberts, died on the way back.
    – J Asia
    Oct 20, 2017 at 16:55

3 Answers 3


The Portuguese were the first westerners to reside in (then) Siam (now) Thailand. The Portuguese embassy is the oldest embassy in the kingdom, and now a monument. Do mind that the relations go back 500 years. As such they enjoyed, at that time, a special status. By the time this treaty was signed, it was purely honorary. By then Portugal was no longer an important power.


Portugal had trading relations in Southeast Asia going back to the 16th century. The main Portuguese outpost was Macau, off the coast of China, but Siam was also an important "port of call."

Either the Thais or the Americans (or both) may have felt more comfortable in Portuguese than in the other party's language.


Courtesy of the Library of Congress, here are some excerpts from a transcript of the Roberts Treaty of 1833:

This Treaty is concluded on wednesday the last of the fourth month of the year 1194 called Pimarông chattavasok (or the year of the Dragon) corresponding to the twentieth day of March, in the year of our Lord 1833. One original is written in Siamese, the other in English; but as the Siamese are ignorant of English, and the Americans of Siamese, a Portuguese & a Chinese translation are annexed, to serve as testimony to the contents of the Treaty. The writing is of the same tenor & date in all the languages aforesaid: it is signed on the one part, with the name of the Chau-Phaya Phraklang, and sealed with the seal of the Lotus flower of glass; on the other part it is signed with the name of Edmund Roberts, and sealed with a seal containing an Eagle and stars.

ARTICLE X. If hereafter any foreign Nation, other than the Portuguese, shall request and obtain His Majesty's consent to the appointment of Consuls to reside in Siam, the United States shall be at liberty to appoint Consuls to reside in Siam, equally with such other foreign Nation.


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