The Ark in the movie was the Ark of the Covenant (the gilded gopher wood box built by Moses on the instructions of God); as such it contained the fragments of the original tablets of the Law, a jar...
The movie was released in on June 12, 1981. The movie itself takes place in 1936.
June 12, 1981.
It was filmed in 1981.
Steven Spielberg directed all four Indiana Jones movies, the first one being Raiders of the Lost Ark (1981).