The people commonly known as Siamese call themselves Thăi which (in the form Tai) appears to be the racial name of several tribes who can be traced to the southern provinces of China. They spread thence, in fanlike fashion, from Laos to Assam, and the middle section ultimately descended the Menam to the sea. The Siamese claim to have assumed the name Thăi (free) after they threw off the yoke of the Cambojans, but this derivation is more acceptable to politics than to ethnology. The territories which they inhabited were known as Siem, Syâm or Syâma, which is commonly identified with the Sanskrit Śyâma, dark or brown[189]. But the names Shan and A-hom seem to be variants of the same word and Śyâma is possibly not its origin but a learned and artificial distortion[190]. The Lao were another division of the same race who occupied the country now called Laos before the Tai had moved into Siam. This movement was gradual and until the beginning of the twelfth century they merely established small principalities, the principal of which was Lamphun[191], on the western arm of the Mekong. They gradually penetrated into the kingdoms of Svankalok, Sukhothai[192] and Lavo (Lophburi) which then were vassals of Camboja, and they were reinforced by another body of Tais which moved southwards early in the twelfth century. For some time the Cambojan Empire made a successful effort to control these immigrants but in the latter part of the thirteenth century the Siamese definitely shook off its yoke and founded an independent state with its capital at Sukhothai. There was probably some connection between these events and the southern expeditions of Khubilai Khan who in 1254 conquered Talifu and set the Tai tribes in motion. The history of their rule in Siam may be briefly described as a succession of three kingdoms with capitals at Sukhothai, Ayuthia and Bangkok respectively. Like the Burmese, the Siamese have annals or chronicles. They fall into two divisions, the chronicles[193] of the northern kingdom in three volumes which go down to the foundation of Ayuthia and are admitted even by the Siamese to be mostly fabulous, and the later annals in 40 volumes which were rearranged after the sack of Ayuthia in 1767 but claim to begin with the foundation of the city. Various opinions have been expressed as to their trustworthiness[194], but it is allowed by all that they must be used with caution. More authoritative but not very early are the inscriptions set up by various kings, of which a considerable number have been published and translated[195].