In the north of the Chao Phraya and its tributaries, the Thais formed themselves into the kingdom of Chiang Saen, the principality of Payao, and other principalities. The Thai chronicles praise Prince Phrom as a heroic king of the Thais who lived towards the end of the eleventh century. With his army, he attacked the Kher empire and conquered its territory down to Chalieng. Having extended his power as far as Lanna, Luan Prabang, Vientiane and Lanchang, he founded the City of Fang for himself to rule and named it Chai Prakan. His successors, hower, failed to keep the kingdom intact, and it came to a tragic end after a short period of time. Later one of Phrom’s descendants created the principality of Payao. Contemporaneously some of the Thai chieftains who were under the Khmer vassalage, such as Khun Bang Klang Thao and Khun Pha Muang, showed signs of independence towards the Khmers.