Ed Eyestone is not one for hyperbole. A cleareyed coach and two-time Olympian, he will casually describe his athletes’ 23-mile training runs in a way that makes it sound as if they had gone for brisk walks. He understands that hard training is a part of the profession and that marathons are inherently challenging, so why oversell the struggle?

But ask him about the marathon course at the Paris Olympics, and Eyestone speaks with a sort of reverence that borders on fear.

“This marathon,” he said, “will have a debris field in the final miles.”

Over the past two weeks, thousands of Olympians have tackled the seemingly impossible. Gymnasts have tumbled on 4-inch beams. Skateboarders have gone airborne over rails and ramps. Triathletes have submerged themselves in bacteria-infested waters.

But Paris 2024 organizers may have saved the most sadistic test for last.

Over 26.2 grueling miles this weekend, Olympic marathoners will be forced to contend with a series of steep climbs and quad-crushing downhills that comprise what is almost certainly the most difficult marathon course in the history of the Games.

The challenge, as always, is the pursuit of glory.

The true goal, more likely, will be survival.

“Oh, my gosh,” the Canadian marathoner Malindi Elmore recalled telling her husband when she got her first look at the course in February, “this looks ridiculous.”