The earliest known reports of these unusual triangles can be traced to the Dutch East Indies in the late 1890s, around 10 years prior to the Wright Brothers' first powered airplane flight in 1903. … What initiated Marler's research was a wave of triangle UFOs in 1990 that occurred in Belgium, where military authorities publicly confirmed the sightings and endorsed the fact that strange vehicles were operating in their skies — extremely similar to flying triangles seen by … …

Excerpt from:
Triangle UFOs Fly In The Face Of Logic – Huffington Post