How many movies have Erich Kettelhut and Fritz Lang collaborated on?

They have worked on 7 movies together! Their first movie together was The Indian Tomb, Part I: The Mission of the Yogi (1921) while their highest rated movie together was Metropolis (1927). They have not worked together since The 1,000 Eyes of Dr. Mabuse (1960). They are most known for their drama films together.