The founding of Chiang Rai is described in the Chiang Mai chronicle in the translation of late David K. Wyatt.
Not long afterwards, the auspicious elephant of King Mangrai ran loose north of a mountain to the east. The king followed the track of the elephant and beheld a country on the banks of the Kok River, flanked by a single beauteous hill. He thought, "When Grandfather Lao Cong built a home for / my Grandfather Lao Kao, I heard that it was [founded] at the base of Mount Pha Rao. When Grandfather Lao Khriang built M. Ngoen Yang, he built it nestled between three mountains, namely Dòi Thung, Dòi Tha, and Dòi Ya Thao, which was very good, so I should likewise make [mountains] the navel of the town in its center. So King Mangrai / built a [fortified] city around Dòi Còm Thòng, which he made the center of the city. It was built in the tao set year, 624 of the Era (1262/63), and was named Chiang Rai.