During the reign of the hero-King Rama Khamheng (Phra Ruang) the country reached the zenith of its greatness and when he died, about A.D. 1090, he left to his heir an empire which embraced much of the Lao states to the north and all of the more southern Khmer kingdoms of Siam. This heritage, however, was fated to endure but a short time. During the eleventh century the Khmer King of Lopburi and the Lao King of Lamphun, both vassals of Phra Ruang, had been intermittently at war with each other without interference from the suzerain; toward the end of the century Lopburi was finally overcome and, declaring itself subordinate to Lamphun, was forced to admit large numbers of Lao to settle within its borders. Soon after Phra Ruang's death, a great Lao army composed of the warriors of several allied states and led by a chief known as Suthammarat, invaded Sukhothai-Sawankhalok itself, defeated its armies, overran its lands to the south, reduced the cities, and founded the capital of Pitsanulok, southwest of Sukhothai and in the heart of the Khmer Kingdom. Thereafter, although the rulers of Sukhothai-Sawankhalok continued for some time to maintain regal state, they were never again to hold a paramount position and were, in fact, to become mere vassals of the ancient enemy until eventually, some four centuries subsequent to the foundation of Pitsanulok, they were to be no more than provincial governors representative of the kings of Ayuthia. Suthammarat, an admirer of the Khmer, in setting up his throne in the conquered kingdom, imitated as closely as possible the ways of Sukhothai and, by marrying a lady of the country, set an example for his following which gave great impetus to that fusion of Lao and Khmer which, already begun in Lopburi, was soon to result in the evolution of the Thai (Siamese) race.