via Bangkok Post, 05 December 2019: The late King Bhumibol of Thailand’s visit to Si Satchanalai in 1958 started an awareness and appreciation of the ancient ruins that led to its listing as a Unesco World Heritage site in 1991.
At the time, Si Satchanalai and the surrounding area was not yet designated a historical park. The monuments themselves were yet to be restored. The royal trip in 1958 played an important role in making that happen.
King Bhumibol made two more visits to Si Satchanalai, in 1966 and 1972.
The historical parks of Sukhothai and Si Satchanalai were officially opened in 1988 and 1990, respectively. Both were collectively listed by Unesco as World Heritage sites in 1991.