Thonburi, the answer to the question, was the kingdom in which Taksin was executed. This kingdom was founded by Taksin himself in 1768, and it succeeded the Ayutthaya Kingdom, which had been destroyed by the Burmese. Thonburi served as the capital of Siam until 1782 when it was replaced by Bangkok.
The Taksin Trailblazer: A Quiz on the Enigmatic Ruler of Thonburi Kingdom