The Unknown Soldier of World War I was buried here in 1920, and three years later the Eternal Flame was kindled.
In 1920, this became the burial place for World War I's Unknown Soldier. 
mnli hypothesis: In 1920, this became the burial place for World War I's Unknown Soldier.  premise: The Unknown Soldier of World War I was buried here in 1920, and three years later the Eternal Flame was kindled.