Today the swashbuckling Planetary Romance, or sword and planet yarn as some have taken to calling it, is synonymous with the stories of Edgar Rice Burroughs. When he burst onto the scene in 1912 with his story Under the Moons of Mars, written under the name Norman Bean, he set the standard for outré Ruritanian adventures. So it's easy to forget that he wasn't the first to write stories like that.
The most well known of his forerunners was Edwin L. Arnold , the author of the 1905 novel Lieut. Gulliver Jones: His Vacation which was later reprinted as Gulliver of Mars. It tells the story of the eponymous swabby who comes into possession of a magic carpet that whisks him of to Mars where he engages in swashbuckling adventures to win the hand of Princess Heru. Recently he appeared in Alan Moore and Kevin O'Neill's comic book, The League of Extraordinary Gentlemen.
Less well known but just as significant is Frank Atkin's novel, A Trip to Mars (1909), which he wrote under the name Fenton Ash. In this adventure, two Earth boys witness a UFO which turns out to be a Martian spaceship that takes then to the red planet where they encounter super science wonders like flying yachts and become embroiled in a war.
Both of these books anticipate much of what later made ERB famous. Yet today they're all but forgotten. When there was a brief revival of the sub-genre in the sixties and seventies it took the form of pastiches of ERB with scarcely a nod to these earlier works.