The phrase "a marathon at" is correct and usable in written English.
It can be used when referring to a specific location or event where a marathon is taking place.
Example: "I signed up for a marathon at the city park next month."
Alternatives: "a race at" or "a run at".
I'd love to try and do a marathon at some point.
I'm impressed that I could run a marathon at all with a body like that.
It is a marathon at most clubs, but just another night at Smalls.
But when you bomb a marathon, at the finishing line, you can guarantee certain marathon-specific things.
He goes to the gym and is training for a marathon, at least "in my head," he said.
Compare that with, say, running a marathon at an average pace of less than five minutes a mile.
Creator, under a brilliant ride from precocious Irad Ortiz Jr., all but flew past as he split horses and overtook Destin by a nose in the final stride of the mile-and-a-half marathon at Belmont Park.
He scoffed at the notion that Spectacular Bid could flunk the Test of the Champion, as the mile-and-a-half marathon at Belmont is known.
Drooker recalled his first thoughts after hearing the news from Boston: "A bomb at a marathon, right at the finish line of a festive occasion — it seemed almost like a mixed metaphor, incongruous and absurd.
Ivan Neville, Cassandra Wilson, Lou Reed, below, and Laurie Anderson are among more than 20 popular musicians scheduled to perform today at a marathon festival at SummerStage in Central Park to support programs that provide health care for musicians in the New Orleans area.
He began bouncing on the balls of his feet, shuffling joylessly at first, like a marathon dancer at ten to midnight, but then with more speed, more pleasure.
