Why is there an eternal flame at the arc de triomphe?

The flame was meant to honor the tomb of the unknown soldier, as a symbol of all the soldiers who lost their lives for the defence of France. It was first lit on November 11th, 1923, and a ceremony was held everyday since then, even when Paris was occupied during WWII. Students and popular demonstrations were held on the 11 of November during WWII, in defiance of the German army and the ceremony gained then a patriotic undertone.

The ceremony is held everyday at 18:30.