They began in the dark. At 5:45 a.m. local time Saturday, three elite marathoners set off on a 26.2-mile run around a nearly flat 1.5-mile Formula One race track in Monza, Italy. This wasn’t a traditional race. Instead, it was a highly orchestrated attempt to break the marathon’s two-hour barrier — an enormous stretch goal that would require slicing nearly three minutes, or 2.5 percent, off the current world record of 2:02:57.

And they almost did it.

Saturday’s attempt was engineered by Nike researchers and involved three runners: Kenyan Eliud Kipchoge, who set his marathon personal best, 2:03:05, in last year’s London Marathon; Eritrean Zersenay Tadese, the world record holder in the half-marathon; and Ethiopian Lelisa Desisa, a two-time winner of the Boston Marathon.

The Nike project, called Breaking2, sought to break two hours with a multipronged approach that included an ideal course (no hills or corners), conducive weather (calm and about 53 degrees Fahrenheit), optimized fueling, pacing set by a Tesla and a rotating group of runners situated to block wind, and of course, high-tech shoes purported to improve running efficiency by as much as 4 percent.

The event was live-streamed on Twitter in what amounted to a two-hour Nike commercial, for which the company brought in star commentators like track great Carl Lewis, women’s marathon world record holder Paula Radcliffe and comedian Kevin Hart.

The race began mostly as planned, with runners keeping fairly close to the necessary 2.51 minutes per kilometer (4:34.5 minutes per mile) pace for the first five of the marathon’s 42.195 kilometers. But by the halfway point, Desisa and then Tadese had fallen off the pace and dropped behind the pace group.

So we have not quite made it to halfway and 2 out of 3 are done…. Performance is hard…We don't know as much as we think we do in Science — Steve Magness (@stevemagness) May 6, 2017

Kipchoge persisted with the pace car and remained within two seconds of sub-two-hour pace at the 30-kilometer mark. After that, he began to fade, but only slightly. After 35 kilometers, he was only six seconds off the record pace, but when Kipchoge crossed the finish line (where marathon legend Joan Benoit Samuelson held the tape), the clock read 2:00:25.

It wasn’t a sub-two run, but it was damn close, and it was the fastest recorded marathon time. (It’s ineligible for a world record, though, because Kipchoge had the benefit of the pace car and pacing crew.) Tadese and Desisa finished their runs in 2:06:51 and 2:14:10, respectively.

Kipchoge’s run was almost perfectly paced, said South African sports scientist Ross Tucker, whose work has shown that even pacing is the optimal strategy. “You look at this chart, look at those kilometer paces,” he said. “Unbelievably consistent, and that’s perfect. Only from 35 kilometers did he slow, and then by 2 seconds per kilometer!”

He’s referring to the chart here, which shows Kipchoge’s 5-kilometer splits compared with the target pacing that would allow him to hit the sub-two-hour mark:

Almost no experts had expected the two-hour barrier to fall in this attempt. Michael Joyner, a human performance expert at the Mayo Clinic who published a paper in 1991 predicting that a 1:57:58 marathon was “physiologically possible,” told me before Saturday’s event that he expected the top finisher to run in the neighborhood of 2:01:30. That Kipchoge came so incredibly close to the two-hour mark should inspire more such attempts, Joyner said afterward.

Ultimately, Saturday’s Breaking2 event was more than just a publicity stunt. It was also a real-world test of the promises that companies like Nike make about the power of science and technology to enhance human performance. The results leave plenty of questions, however. Sure, Kipchoge had a spectacular run, but it’s almost impossible to say how much was the shoes and other technology and how much was his incredible talent. And it’s important to note that the two other runners underperformed relative to expectations, Tucker said. “I reckon it’s a wash, myself.”

One thing is clear: Kipchoge is among the greatest marathoners of all time, and he’ll have a crowd of fans watching to see what he does next.