There was a time when Cheltenham, too, resembled a fortress. Irish horses would steal the odd prize, but basically all they were doing was kicking a wet ball high into the gale and sending in the scavengers. Nowadays, however, they have fleet runners who can weave through a clumsy home defence with all the flamboyance of Brian O'Driscoll himself.
In 1987 and 1988, the Irish successively mustered just one winner each year. Things reached a nadir in 1989, when they were wiped out altogether.
In those days, all their most promising young horses were routinely sold to British buyers. Since then, the predators have gradually been driven away by the growing economic strength of the Celtic Tiger.
Last year, when the Festival was extended to a fourth day, the Irish won nine of the 24 races.
Michael Hourigan, who trains the leading Irish candidate for the Totesport Cheltenham Gold Cup, knows that Beef Or Salmon might once have found his way to Britain. A veteran horse-dealer himself, he is well placed to measure the change in the marketplace.
"We can stand up to them now," he said. "You take an Irishman into the yard, you show him the horse, and if he likes it he'll buy it off you. The Englishman says he will go to another yard and be in touch. Well, if he asks about a horse these days, the chances are there's an Irishman who's bought it already."
Last year, the Irish achieved the equivalent of a Triple Crown by exporting the meeting's three greatest prizes: the Champion Hurdle with Hardy Eustace, the Queen Mother Champion Chase with Moscow Flyer, and the Gold Cup with Kicking King.
True, all three have had trouble preserving their dominion since. Kicking King is injured, while many have perceived signs of deterioration in both Hardy Eustace and Moscow Flyer. The performance of these two ageing champions is the cornerstone of the meeting this year. Both ran poorly on their latest start, but each has won three times at the Festival and few will desert them with a clear conscience.
Ah, to be sure, to be sure: if only we could be sure. Horses do not deal in crude absolutes. It is mankind that simplifies the challenge, reduces things to black and white - or rather to green, white and orange. At Cheltenham patriotism is not just the last refuge of the scoundrel, but also of the hopelessly bewildered.
The perplexities of the formbook can be conveniently supplanted by a primal, tribal longing. This is traditionally vested in one or two horses identified as "the Irish bankers".
If the Irish at Cheltenham sometimes feel prey to patronising Oirish caricature, they are at least partly responsible themselves. There is something visceral, something helpless, about their commitment to these particular animals.
As is often the case, the Irish banker this year contests the very first race of the meeting, the AIB Supreme Novices' Hurdle. It was James Joyce - not, admittedly, the sort of Irishman you would expect to find here - who played on the kinship between "funeral" and "fun-for-all". In the circumstances, this horse could scarcely be better named: Sweet Wake.
For around 7,000 Irishmen at Cheltenham, and countless more at home, the first four minutes of the Festival will either convey them to fortune, or plunge them into the abyss.
And no matter how things turn out, the likelihood is that Sweet Wake will maintain the suspense at least for the first three of those minutes. The five-year-old is ridden by Paul Carberry, whose exquisite balance tends to make horses look as though they are travelling far more powerfully than sometimes proves to be the case.
Sweet Wake, trained by Noel Meade, was a classy runner on the Flat in Germany and has cantered home in both his starts over hurdles, but he can scarcely be expected to win this race without breaking sweat. His response when Carberry asks him to knuckle down for the first time will be the defining moment of the meeting.
The bookmaking industry is hoping to strike £500m of bets during the next four afternoons. On the course alone, betting turnover last year reached £50m. That represents a dangerous combination with the 170,000 pints of stout served during the same period.
For all the bacchanalia, for all the emotion, Cheltenham is a deadly serious business. And anyone wishing to approach it in that spirit should proceed directly to Ladbrokes and take the odds of 5-6 about the Irish having seven winners or more.