The first Thai flag was used in the Ayutthaya period. It was developed from a plain red plain flag on ships to mark that they belonged to Thailand. Later, in the reign of King Phraphutta Yodfa Chulalok (King Rama I), he came up with an idea about how to differentiate between Royal ships and civil ships. He gave the order to change the flag for Royal ships to be a plain red field with a white Sudarshana Chakra of Vishnu. It was used in the early Rattanakosin period.
In 1916, King Mongkut Klao Chao Yu Hua (King Rama VI) had the wisdom to enact the Flag Act, B.E. 2460 (1917) and named the flag “Thong Trai Rong.” The Flag Act was amended in 1936 and is used to this day.
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