This afternoon, in 2.5 minutes of blurred action on the outskirts of Paris, the landscape of the modern thoroughbred could be changed for ever. If Sea The Stars adds the Arc to his victories in the 2,000 Guineas and Derby, he will recalibrate the measurement of greatness in racing and become the most valuable thoroughbred in the history of the turf.

No other horse, not Nijinsky, Sea Bird, Mill Reef or Dancing Brave, has won the 2,000 Guineas, the Derby and the Arc. If Sea The Stars completes that unique treble, the modern Triple Crown, there will be no argument; he will be, as the Italians put it, the Campionissimo, the champion of champions.

He can do it, too. Take the word of three Arc-winning jockeys. “You have to compare Sea The Stars with Nijinsky,” said Lester Piggott (Rheingold and Alleged, twice) last week. “He has it all, speed, stamina and loads of class. He’s a good thing. Just look at the betting.”

Or Pat Eddery (Detroit, Rainbow Quest, Dancing Brave, Trempolino): “I can’t see anything beating him. A horse like him comes along only once in a lifetime.”

Or Walter Swinburn (All Along): “If he was going to be beaten at any time, it would have been in the 2,000 Guineas. He’s in good hands, so, with any sort of luck, I don’t see him being beaten.”

Even with the natural goodwill generated by Sea The Stars, such uniformity of opinion is rare in racing, though questions will still lurk in the mind of John Oxx, his wise old owl of a trainer, just as they did before the Guineas and the Derby. Will the ground be right? Will Sea The Stars have a clear run in a notoriously hazardous race? Can the horse maintain his form so deep into a season that began in May and has included five Group One victories in five months?

The bookmakers’ answer — a best quote of 4-5 with Corals — is emphatic enough and the omens look good. The ground should be ideal and the draw, stall six in a field of 19, has been kind. Fame And Glory, runaway winner of the Irish Derby; Conduit, winner of the King George; and the French pair of Stacelita and Vision d’Etat have already been relegated to the role of extras. Even Andre Fabre, the acknowledged wizard of the Arc, has said he will be honoured if his horse, Cavalryman, finishes second to Sea The Stars. He might do well to ask Aidan O’Brien how that feels. Like some war-weary general, O’Brien has pitched 12 horses against Sea The Stars this term and returned home defeated every time. There is barely an inmate at Ballydoyle who could not give you a detailed description of the gleaming bay backside of Sea The Stars.

Win or lose, today will be the last we see of Sea The Stars, on this side of the Atlantic at least. He is bound for a lucrative stud career sooner rather than later. Already, though, he has left a treasure trove of memories. Recently Oxx, as much a part of the story as his wonder horse, has recalled the sense of awe that greets his imposing champion on the gallops every morning. “You see the lads from other stables talking to each other,” he says. “There’s a feeling there’s something special around.” This is The Curragh, remember, where they have seen a few decent horses down the years.

The same aura permeated the gentle slopes of Sandown on Eclipse day when Sea The Stars emerged from the stables taut and gleaming like a prizefighter, turning every head and hushing all conversation. As he strode into the main paddock, the crowd broke into spontaneous applause. “You don’t have to be a great judge of a horse to know he’s got it,” said Mick Kinane, his jockey. “What’s more, he knows it, too.” So does Kinane, 50 last June, whose smile will last long after he has removed his riding boots for the final time.

Behind the scenes, Kinane’s experience has been critical to the faultless handling of the campaign. When Oxx’s courage has failed him, most notably in doubting Sea The Stars’ stamina in the lead-up to the Derby, Kinane has stepped in, brimming with confidence and moulding races to his will as only the very best can. Sea The Stars’ natural speed helped, but Kinane has used his judgment of pace and his acute tactical brain to master the various demands of the straight mile at Newmarket, the downlands at Epsom and the deceptive contours of Sandown and York.

Today, Sea The Stars takes the most important test of his young life. To be remembered in England, you have to win the Derby; to be remembered in France, you have to win an Arc. To be mentioned in the same breath as Mill Reef and Sea Bird, you have to win both. Troy, Generous, Authorized, Reference Point, all Derby winners, have come into the Arc as “unbeatable” favourites and all have found it a race too far.

“You wouldn’t want to put Sea The Stars up there until it’s happened,” says Sir Peter O’Sullevan. “But if he does win, he’s got to be up there with the very best. It’s a pretty daunting effort what he’s done, winning a Guineas and a Derby and keeping going through a long season. He’s not shirked anything.