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 [th]. 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 [th] 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.

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 confederatin 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.

Under the name of Xiānluó hú or Xiānluó, the state performed 41 tributary missions to the Chinese court during the Hongwu era, 33 in the name of Xiānluó hú and as Xiānluó for the remaining. In the era of Ankorian king Jayavarman VII (r.1181–1218), an inscription called Prasat Phra Khan (จารึกปราสาทพระขรรค์) was made, among others, the name Suvarnapura is mentioned, which has been identified with Suphanburi.

Modern scholars believe Suphannabhum was Chen Li Fu mentioned in the Chinese Sung Hui Yao Kao in 1200 and 1205.

According to the local legends, Suphannabhum is the succeeding state of an ancient port city of Mueang Uthong, which evolved into complex state societies around 300 C.E. Since the river leading to the sea was dried up in places, shallow, and consequently not navigable, and also due to some pandemics, Uthong lost its influence as the trading hub; the city was then abandoned around the 11th century and the people then moved to resettle in the present day Suphanburi. This timeline corresponds with that the Tambralinga's king Sujita seized Lavo and was said to conquer the Mons of the Menam Valley and the upper Malay peninsula in the 10th century, the 9-year civil wars in the Angkor in the early 11th century, which led to the devastation of Lavo, as well as the Pagan invasion of Lavo around the mid-10th century. All of these are probably the causes of the fall of Mueang Uthong.

This region has been claimed to be the legendary Suvarnabhumi by several local scholars. Numerous ruins and artifacts from the Dvaravati period have been discovered around the area. However, contemporary documents from this period are sparse; the available material consists primarily of local chronicles and legends.

Paul Wheatley suggests that the city-state of Chin Lin which was mentioned in the Chinese archives of the Liang dynasty as the state that was Fan Man, the Great King of Funan Kingdom, attempt to conquer in the 4th century CE, might be located in west central Thailand, since the word "Chin Lin" 金鄰/金邻 means "Land of Gold" or "Suvarnabhumi"; as mentioned in the archive, it was a state located approximately 2,000 li (800 kilometers) west of the Funan Kingdom, which corresponded to the area where is now central Thailand.

According to the Northern Chronicle [th], the region's political center from the 9th to 12th centuries was located at the old Kanchanaburi city ruins but local legends suggest it was in the old town Nakhon Pathom (formerly known as Nakhon Chaisri), which has been speculated to be the center of Dvaravati. As per Chalerm Kanchanakam's calculations based on the text provided in the Yonok Chronicle, which states that Phraya Phan, the founder of Suphan Buri, ascended to rule Haripuñjaya in 913, it is estimated that Suphan Buri was founded around 877–883.