Suphannabhum or Suvarnabhumi; later known as Suphan Buri (Thai: สุพรรณภูมิ or สุพรรณบุรี) was a Siamese city-state, that emerged in the early "Siam proper" which stretched from present-day west central Thailand to the north of the Kra Isthmus, with key historical sites at Uthong, Nakhon Pathom, Suphan Buri, and Ban Don Ta Phet. The kingdom is referred to as Xiān in the Chinese records since 1349, but according to the archaeological evidence in Suphan Buri, it was speculated to have emerged around the mid-12th century. However, a calculation made by Borihan Thepthani based on the information provided in the Northern Chronicle says that the city of Suphan Buri was founded in 877 and became a free city-state after its suzerain, Nakhon Pathom of Kamalanka, fell to Phetchaburi in 913. Japanese scholar Tatsuo Hoshino has proposed that Suphannabhum was identified in Chinese sources as Shě Bá Ruò (舍跋若), which he further interprets as the western terminus of a trans-Mekong trade confederation in the 9th century. According to this hypothesis, the confederation comprised five polities: Pó Àn (婆岸), identified with Mueang Phon; Zhān Bó, associated with Champasri; Qiān Zhī Fú, identified with Si Thep; Mó Là (摩臘), located in the coastal region of Champa; and Shě Bá Ruò, corresponding to Suphanburi.
Suphannabhum became the center of Xiān, succeeding Phip Phli, no later than 1349, when Xiān was defeated by Luó hú (Lavo) and the tribute sent to China under the name of Xiānluó hú (Siam-Lavo or Ayutthaya Kingdom) was led by Xiān's King of Su-men-bang, in which Su-men-bang has been identified with Suphanburi. Since then, it was one of the states under the mandala confederation of Ayutthaya Kingdom and was completely merged to the Ayutthaya in 1438. However, modern scholars suggest Xiān mentioned in the Chinese and Đại Việt sources since the 11th century potentially was Ayodhya, a polity that later known as the Ayutthaya Kingdom (Xiānluó hú or Xiānluó) in the mid-14th century.
