Aided by the massive influx of Thais, the Thai principalities were able to throw off Khmer control. In 1257 the first Thai kingdom, Sukhothai, was founded by King Sri Intratitya. Under his son, King Ramkamhaeng (reigned 1277–1317), the Thais began adopting many Khmer ways, including their religion, Theravada Buddhism. Ramkamhaeng strengthened the kingdom and extended its boundaries southward to the Malay Peninsula, conquering the weak Mon kingdom. Sukhothai dominance was short-lived, however, lasting little more than a century.