The running giant recruited three of the greatest marathon runners to ever live—Eliud Kipchoge, Lelisa Desisa, and Zersenay Tadese—and set their sights on the thought-to-be-impossible task, planning a race on auto racing track in Monza, Italy with the ideal mix of altitude, temperature, vapor pressure, course shape and elevation. The Nike team studied VO2 maxes, running economy and every other aspect of the athletes' physical capacities to fine-tune their training. Nike arranged pacing crews of other champion distance runners to keep the Breaking2 runners on speed and reduce their wind resistance. And, Nike being Nike, it made a shoe.

Prior to Breaking2, the running shoe market was mostly dominated by designs that kept shoes lightweight and low to the ground. Racing flats and "minimal" shoes aimed, essentially, to replicate the effects of running barefoot or close to it. Nike flipped that idea on its head, predicting that a "more is more" approach, with a much larger and smartly-designed cushion would provide better energy return and propulsion while also offering greater comfort for athletes pounding their feet on concrete at such high speeds for such great distances.

Using a new kind of lighter and softer foam that it called ZoomX, Nike built its new marathon shoe with a relatively tall 21mm forefoot stack. And since a stiffer sole can have positive effects on running economy, Nike added—into the foam—a curved carbon fiber plate, which was designed with a particular geometry and stiffness level to reduce energy loss when a runner bends at the toe. Theoretically, that allows for more forward propulsion on each foot strike.

The resulting shoe was paired with custom-designed sock-style Flyknit uppers, fitted specifically for each of the three athletes in Breaking2, and dubbed the Zoom Vaporfly Elite—a kind of concept car version of what would later become a retail-ready offering from Nike. The prominently thick sole—with a swoosh stretched across the midfoot and down onto the foam—cut a distinctive silhouette in Nike's media blitz leading up to the race. While the spirit of Breaking2 purported to be more about the spirit of challenge and redefining the impossible than about selling shoes, Nike didn't waste any time publicizing its breakthrough running sneaker.

In the early morning hours of Saturday, May 6, 2017 the runners took to the starting line. After its own months-long media push and excited coverage from running (and sneaker) publications, Nike live-streamed the attempt (and later that summer, used the footage in a documentary made with National Geographic). Despite all of the science and shoe technology and the athletes' groundbreaking athleticism, though, the 2 hour ceiling remained unbroken. Lelisa lost momentum and finished at a relatively slow 2:14:10. Zersenay stayed strong throughout the race but finished with a 2:06:51, beating his personal best by nearly four minutes, a staggering improvement for a runner at that level but still, of course, shy of the goal. Eliud Kipchoge, arguably the greatest distance runner to have ever lived, took a commanding lead and left the other two runners in his wake, keeping an incredible pace clear through to the end—but it was not quite enough. Kipchoge finished with a time of 2:00:25.

While it wasn't a sub-two-hour run, the result was incredible nonetheless. Kipchoge beat the world marathon record by two minutes and thirty two seconds, a huge margin by elite marathon standards. The downside: The race did not quality as an official marathon under the International Association of Athletics Federations' rules, due primarily to Nike's use of multiple pacing teams (who would swap on and off the course so as to keep up with the Breaking2 athletes). Critics also complained that these pacers, plus the race's pacing car that carried a tall digital clock, offered an unfair wind-breaking advantage, and that the staggering time was less a measure of Nike's shoe technology and athlete training more than it was a combination of advantages that official marathons don't have.

Still, the results speak for themselves: A 2:00:25 marathon is an almost unbelievable feat, no matter the circumstances, and Nike leaned in hard to the design that it claimed helped make such a time possible. That summer, it brought the technology to the market.

First, and truest to the Breaking2 shoes, was the Zoom Vaporfly 4%: A mass-market release of the same technology that Eliud and his fellow runners wore, with the same ultra lightweight ZoomX sole and carbon-fiber plate. It was so named for the 4% improvement in running economy the shoe claimed to offer compared to Nike's previous, fastest racing flat (a number that may seem low, but is actually hugely significant for elite-level athletes who battle for fractional improvements). Demand for the Vaporfly 4% was massive and its release was limited, turning the shoe into an instant grail within the running community.

While the Vaporfly 4% retailed for $250 and was nearly impossible to obtain, Nike's second Breaking2-inspired offering, the Zoom Fly, was more amateur-friendly. At $150 and with a much wider release, the Zoom Fly used the same general design and technology as its higher-end cousin, but had a Lunarlon foam midsole (not quite as light as the ZoomX, but more durable) and a nylon (rather than carbon fiber) plate. It quickly became popular as a fast and exceedingly comfortable shoe accessible to both casual runners and intense amateur athletes, and Nike slowly began to release new colorways in addition to the "Ice Blue/Bright Crimson/University Red/Blue Fox" that led all of the Breaking2 shoes' promotional imagery.

Despite its singular focus on running performance, the shoe's profile quickly became a style touchstone as well. The Zoom Vaporfly Elite, born as a breakthrough for top-tier runners with a design that was far from anything in the streetwear world, had come full circle to create a shoe profile that Nike could sell to both athletes and athleisure fans. “Foundationally, the Zoom Vaporfly Elite is appealing, because it authentically advances sport,” Nike sportswear designer Nathan Schultze says. “For us, its aesthetic resonates culturally, well beyond its original intention.”

With the Vapor Street and the Zoom Fly SP variants before it (whose translucent uppers, while cool, feel too fragile to be reliable for serious running), Nike has done again what they've become so masterful at in the past: pushing the technical boundaries of athletic gear, then promoting their design as a style item that reaches well beyond its origins on a track, road, field, or court.

So you don't need marathon ambitions—let alone sub-two-hour ones—to wear a Breaking2 shoe. Though if you do, these (and its many variants) might help you get there.