One of the first “movies” ever, the Lumière brothers’ L’arrivée d’un train en gare de La Ciotat or The Arrival of a Train at La Ciotat Station.  It was probably shot in 1895 and first exhibited in 1896.  From the beginning filmmakers played with 3D–trying to break the proscenium wall of theatre with the new technology of film.

Louis Lumière later re-shot this in 3D (either in 1903 or 1935 depending on what account you believe).  There’s a lot more research to be done on the history of 3D!