When it comes to important dates in world history, November 15, 1915 doesn’t particularly stand out to most. For some, however, this day marked the occurrence of a strange, unexplainable event.

At least, according to legend.

By this time, Europe had been embroiled in a war for nearly a year and a half on three fronts. The Western Front had devolved to vicious trench fighting and the occasional use of chemical weapons, the Eastern Front was ebbing and flowing, and the Austrians and Italians were fighting the cold temperatures and altitude, as much as each other, on the Southern Front. The casualties were mounting for all sides when this strange incident supposedly happened.

At 10:30 p.m., as men on all fronts were fighting, hundreds in different locations, from both sides, just laid down their arms. The legend states that all of the men who quit fighting claimed to have seen a bright light in the sky, and then they just lost control of their bodies.

Again, this is a legend, which means that it may or may not be true—or there may be a grain of truth to it. There are not any official government records known to exist that mention the mysterious light, although the chance that any government official would have documented something like that in 1915 is unlikely due to the pressures of war and it just sounding “crazy.”

Still, talk of the incident persisted well into the 1950s. It even provided the plot for an episode of the 1950s television show One Step Beyond.

Those who believe it is nothing more than an urban legend think it started with a soldier seeing something strange. His account then morphed into a much more elaborate story over the decades.

But there are others who think that thousands of soldiers did see something strange in the sky on that evening.

One theory is that the mentally draining nature of warfare, especially trench warfare, induced a mass psychosis across Europe. Mass psychosis has been observed plenty of times throughout history, but this (if true) would be one of the biggest cases.

Then there are the more supernatural explanations.

Some believe it was a sign from god or angels to end the destruction before it was too late, while others think it was visitors from another planet. One thing is for sure, no matter the source of the light (if it even happened), there is little doubt that this story will continue to be told.