How a failed card subtype would lead to the creation of Magic: The Gathering's planeswalker cards.

Planeswalkers are rather well known in the collectible card game Magic: The Gathering.  After all, they've been around (story-wise) since Magic's earliest days and as a physical card type since their debut in 2007's Lowryn.

But, did you know that they owe their existance (in part, at the very least) to an abandoned new card type that was being designed for the set Ravnica: City of Guilds?

The card type was known as "structure" and it was the brain child of MTG's original designer, Richard Garfield.  The idea behind the structure card type is that they were to represent the various buildings found throughout the plane-spanning city of Ravnica.

"They were cards that had an ability -- kind of like an enchantment; they would affect the battlefield -- but they had a toughness," explains Magic head designer Mark Rosewater, who lead the design team for Ravnica: City of Guilds.  "So the idea was that, in order to get rid of them you had to attack them with creatures.  They were kind of like attackable enchantments, which is how Richard envisioned them."

WATCH: MARK ROSEWATER TALKS STRUCTURES AND PLANESWALKERS WITH MAGIC UNTAPPED

Despite the fact that Rosewater and the rest of the team were fans of this new card type, it was never meant to be.  Simply put, there was so much already going on in the three sets that were to make up the Ravnica block -- Ravnica: City of Guilds, Guildpact, and Dissension - that there was no room for it.

Of course, that didn't mean that Magic's designers might not revisit the structure card type at some point in the future.

"I said to Richard I like it...if at some point we find a home for it, I'll keep it in mind," says Rosewater.

Fast forward a year and a half or so.  Wizards of the Coast is now working on the set that would become Future Sight.  Matt Cavotta, who was on both the set's design and development teams, pitches to Rosewater an idea for a planeswalker card type.  The big questions were how to make such a card type and how to make it work within the rules of the game.

That's when structures came back into the conversation.

"We were trying to figure out how to make planeswalkers into cards and the very first thing that came to me was remembering structures from Richard," tells Rosewater.  "So, one of the first things we built into planeswalkers was they were attackable."

This was important because, at the time, there weren't many ways to address this new planeswalker card type.  By making them attackable, players had a de-facto way of dealing with them from the get-go.

Of course, there's more to planeswalker cards than just being attackable by creatures, but it's Garfield's abandoned card type that, in part, made planeswalker cards what players have come to know.