AT FIVE P.M. ON A THURSDAY, the banks of the Seine are bustling. Tourists carrying drippy ice-cream cones parade past the antique booksellers, couples from the Sorbonne lounge between the willow trees, and in the wall-mounted trash cans, mixed in among the sandwich bags and half-eaten macaroons, are the first of the season's champagne bottles. It's springtime in Paris.

The fashion is clearly changing, too. At the Pont des Arts, an iron bridge near the Louvre, I stumble upon a photo shoot overseen by a white-haired man in a high white collar and fingerless gloves. It's clothing designer Karl Lagerfeld. He takes one sip from a goblet of red wine and has his assistant throw the rest in the river. Out with last month's scarves and the color violet; in with hot pants!

I climb the stairs to the 17th-century Hotel des Invalides, and there I find them: a handful of les rollers, the rollerbladers, weaving around little pink cones. They look just like they might have a decade ago, but with less neon.

They swoop and twirl and glide across the glassy-smooth square. A shirtless guy in his mid-twenties, flabby belly jiggling, weaves through the cones on toes and heels, his arms waving like those of a competitor in rhythmic gymnastics. He accidentally knocks over a couple of cones—blonk, blonk—but continues his balletic performance unperturbed, dancing for no one but himself. The winged horses and trumpeting angels of the Pont Alexandra III stare off in the other direction.

I sit down on the esplanade's carved stone bench and ask myself the question I will ask over and over during the next four days: Rollerblading?

A 60-year-old skater with yellowing eyes, wearing the full complement of pads, introduces himself as Marc Delalain. A former oil-futures trader, he started skating roughly a year ago. He practices here several hours a day and just recently took up the slalom. He says that because trinket sellers have displaced skaters from the gentle slopes of the Trocadéro, near the Eiffel Tower, this is now the best place for slalom.

"Slalom is not so easy," he opines, "but with the roller we join another world for the body. Walking, legs are in front; with the roller, legs cross."

His Franglish hangs in the air for all to ponder. When I hint that rollerblading just ain't so cool in America, he looks injured, and I immediately feel bad.

"What do you like about it?" I ask.

"With two feet on the floor, in shoes, you are a lonesome cowboy," he explains. "But with the roller, you are not like that man. Young, old—in roller, we are all the same tribe."