Since the 1940s, when Superman, Batman, and many of the company's other heroes began appearing in stories together, DC's characters inhabited a shared continuity that, decades later, was dubbed the "DC Universe" by fans. With the story "Flash of Two Worlds", in "Flash" No. 123 (September 1961), editor Schwartz (with writer Gardner Fox and artists Infantino and Joe Giella) introduced a concept that allowed slotting the 1930s and 1940s Golden Age heroes into this continuity via the explanation that they lived on an other-dimensional "Earth 2", as opposed to the modern heroes' "Earth 1"—in the process creating the foundation for what was later called the DC Multiverse.