Asimov created the fictional Galactic Empire in the early 1940s based upon the Roman Empire, as a proposal to John W. Campbell, after reading Edward Gibbon's "The History of the Decline and Fall of the Roman Empire" when he was working at the Philadelphia Navy Yard with Robert Heinlein. The concept evolved through short stories and novellas in "Astounding Science Fiction" magazine during the 1940s, culminating in the publication of the "Foundation" stories as a trilogy of books in the early 1950s.