The flag shows five horizontal stripes in the colours red, white, blue, white and red, with the central blue stripe being twice as wide as each of the other four.
The red stands for the land and people, white for religion and blue for the monarchy.
The National Flag is also called the “Tri-Rong”, meaning tricolour.
The first flag used for Siam was probably a plain red one, first used under King Narai (1656–1688).
But the Naval flags later adopted a symbol for the red background of a white chakra, or the Hindu mythological elephant Airavata inside the chakra.
The first Siam flag was created in 1855 by King Mongkut (Rama IV), featuring a white elephant on a red background.
In 1916 two versions of the national flag were declared for use in Siam by King Vajiravudh (Rama VI ). The standing elephant flag was for official purposes and had a white elephant in royal regalia.
Legend has it that the king spotted the flag hanging upside-down, and to prevent this from happening again, he created a new flag for civilian purposes, which was symmetrical
To address the difficulty of making an elephant on the flag appear attractive, the flag was changed to the current design but with the middle colour of the same red as the outer stripe,
Later in 1917, the middle colour was changed to dark blue, a symbol of Thailand's participation in World War I on the side of the Allies and to commemorate King Vajiravudh.
At that time blue was regarded as the auspicious colour for Saturday, the day Vajiravudh was born.
This flag has been continuously used as the national flag of Thailand for both official and civilian purposes ever since.