The Cabinet of Dr. Caligari (1920) is widely considered to be the first true horror film ever made. Writer Hans Janowitz claims to have gotten the idea for the film when he was at a carnival one day. He saw a strange man lurking in the shadows. The next day, he heard that a girl was brutally murdered there. He went to the funeral, and saw the same strange man lurking around. He had no proof that the strange man was the murderer, but he fleshed the whole idea out into his film. (x)

(Source: maudit, via brujeriaa)