Sai Thong Som

The Legend of the Arhat relates that his father Balidhiraja, a son of Kalavarnadisharaja, moved south from Sukhothai about 687 and deposed the reigning monarch of Devapura, after which the throne was given to his younger son Sai Thong Som.^[1]: 3–4 His only recorded sibling is his elder brother Balipatijaya, who acceded at Lavo in 700 in succession to their grandfather Kalavarnadisharaja.^[1]: 4

On the evidence of his name, the Thai historian Manit Vallibhotama proposed that Sai Thong Som was born to a Tai queen consort.^[1]: 5 The suggestion fits the political circumstances of the preceding reign: after his enthronement at Lavo, Kalavarnadisharaja is reported to have extended his influence north into the Tai polity of Chiang Saen,^[1]: 5 which the Northern Chronicle [th] names Nagendhara (Thai: นาเคนทร).^[2]: 25 Intermarriage between the Mon dynasty of Dvaravati and Tai elites is placed within that expansion.^[1]: 5

Tai political weight in the region grew afterwards. By 861 the Tai Yuan, or Tai Chiang Saen (ไทเชียงแสน), are recorded as established at Lavo and increasing in influence there.^[3]: 39

No record survives of Sai Thong Som's immediate successor. Archaeological and textual evidence indicates that by the early 8th century, within the span of his reign, the political predominance of Dvaravati had begun to decline.^[4]: 60 The seat is nonetheless attested after that point in the epigraphic record, under the name Sambuka: the Lopburi inscription K.577, of about the 8th–9th century, names its donor Arushva, chief of the people of Tangura, as the son of the king of Sambuka.^{[5][6]: 68–69, 72} That centre is placed by several scholars at Nakhon Pathom.^{[7]: 24–25, 30} The inscription leaves the king unnamed, and no study has proposed a connection with Sai Thong Som or with any other named ruler.

One account of that decline places the initiative outside the Menam basin. Hiram Woodward, who situates Si Thep within the polity known to the Tang court as Wen Dan, has proposed that a Si Thep powerful enough to dominate the 8th century may have exercised some control over Nakhon Pathom together with Lopburi, U Thong and Khu Bua, and has asked whether central Dvaravati should accordingly be understood as having pre- and post-Wen Dan phases. He offers an alternative in which Dvaravati features at Si Thep resulted from a peaceful movement of monks rather than from conquest, and presents the whole as a possibility rather than a finding.^[8]: 93