We often bring up Roman numerals during Super Bowl time (when at least one sports writer has to come up with something at a deadline), but Slate has a really interesting piece on the popularity of Roman numerals when designating sequels and the like … here’s a bit in medias res:
It began with the greatest sequel of all time, The Godfather Part II. Until the mid-1970s, sequels weren’t usually numbered at all. Instead, they took names like After the Thin Man (1936) and Another Thin Man (1939), or Bride of Frankenstein (1935) and Son of Frankenstein (1939). One of the first sequels was The Fall of a Nation, Thomas F. Dixon’s sequel to the blockbuster The Birth of a Nation. And this continued through the early ’70s. The Planet of the Apes franchise, for instance, used names like Beneath the Planet of the Apes (1970) and Escape from the Planet of the Apes (1971). Even in the rare case that a title was numbered—think of Henry IV Part 2, originally The Second Part of Henry the Fourth—Arabic numerals were used.
The tremendous success of The Godfather Part II, both at the box office and Oscars, would revolutionize Hollywood nomenclature for the next 15 years. There were rumblings of a return to Roman numerals in the lead up to 1974—they were used by the NFL beginning with Super Bowl V in 1971, and by Led Zeppelin starting with Led Zeppelin II in 1969—but after the Godfather sequel Hollywood began to slap a II on just about any hit it could get its hands on. This began with the French Connection II the following May, and continued with movies like Exorcist II in 1977 and Damien: Omen II in 1978. None of these films lived up to the originals at the box office, though, and it wasn’t until Rocky II (1979) and the Star Wars sequels (beginning with Star Wars Episode V: The Empire Strikes Back in 1980) that Roman numerals really took off. [...]
… the Expendables sequel is bucking the trend …