Why ancient cities? Why Mars?
Why is Mars so ancient? Why are Venus’ jungles so thick and swampy? Why do giants come from Jupiter?
The short answer to Mars and the rest is misinformation. That and imagination.
The idea that Mars may have been home to an ancient civilisation was first given popularity through Percival Lowell, who, in Mars (1895), Mars and Its Canals (1906), and Mars As the Abode of Life (1908), gave birth to the idea that Mars’ canals were vast projects completed by an advanced civilisation that appeared to leave no other trace of its existence.
Except there weren’t ever any canals. Percival saw things that later scholars attribute to a mix between terrible telescope optics and fanciful imagination.
But the seed of an idea was planted, one that outstripped all other adventures that had been placed on the red planet. Authors more and more (forgetting the likes of C. S. Lewis and Edgar Rice Burroughs) were beginning to look at the geography of Mars to plan their stories.
Mars looked like a dusty bowl of a planet. But now, it also had some imaginary canals. Take the two, and you have a civilisation that’s died off somehow. The rest, the how and the why we’ll leave up to many authors to imagine.
What a fantastic story framework to begin with. Essentially, this is the story of all science-fictional romances of the past. Sketchy observational science coupled with idealism created a prehistoric Venus filled with dinosaurs simply because the clouds over Venus made the planet look somewhat like a prehistoric Earth.
Jupiter? Well, it’s a giant planet — where else would giants fit in?
Today, it’s somewhat harder to imagine Mars crawling with dead cities. Just as the exploration of all the world’s continents put to bed tales of Lilliputians, so too do we feel increasingly at odds with a populated, or post-populated, Mars.
But that hasn’t stopped fantasy and fantastical science fiction authors from carrying the stories onwards. Percival’s observations were quickly disproved, but his inspired writers outlived his faulty lens.
This means we can still play on Mars even today, although the air is not thin but completely non-existent. Life isn’t hard on Mars. It's non-existent.
But who cares if we’re playing, just as long as we’re aware that’s what we’re doing. The Mars we got is a fantastic playset. So keep the stories coming — but whatever you don’t take off your helmet when you get there.