The DC Multiverse concept was expanded in later years with the DCU having infinite Earths; for example, the Golden Age versions of DC heroes resided on Earth-Two, while DC's Silver Age heroes were from Earth-One. Since "Crisis on Earth-One!" (1963), DC has used the word "Crisis" to describe important crossovers within the DC Multiverse. Over the years, various writers took liberties creating additional parallel Earths as plot devices and to house characters DC had acquired from other companies, making the DC Multiverse a "convoluted mess". DC's comic book sales were also far below those of their competitor Marvel Comics. According to "ComicsAlliance" journalist Chris Sims, "the multiverse . . . felt old-fashioned. . . . Marvel, on the other hand, felt contemporary and when you stack them up against each other, there's one difference that sticks out above anything else: Marvel feels unified."