Whatever happens at the Millennium Stadium this evening – and there is a rich tapestry of possibility, stretching from a first Irish clean sweep in 61 years to a first successful Welsh defence of a championship title in 30 years, with the chance of a damp-squib anti-climax lurking menacingly between the two – the final Six Nations game of the season is likely to live on in the minds and spirits of the participants for a good while yet. If, as Warren Gatland declared this week, the Welsh dislike the Irish even more than they dislike the English, the fighting during the Lions' training sessions in South Africa this summer will make the Test series against the Springboks look like an armistice.
Gatland caused quite a kerfuffle with his comments on the state of oval-ball relations between the Celtic cousins, and just for once in the weird and wonderful world of sport-speak, there can be no suggestion of over-reaction. The head coach of Wales is a New Zealander, not a Celt (although he has spent much of his coaching career in Celtic lands), and might just be forgiven for getting things round his neck. Even so, it was an extraordinary comment.
Gatland will be a senior member of the Lions back-room staff, and he must know that successful Lions tours are built on a bedrock of squad unity. Quite how the likes of Rob Kearney, Brian O'Driscoll, Ronan O'Gara, David Wallace and Jamie Heaslip will now see their personal contests with Lee Byrne, Tom Shanklin, Stephen Jones, Martyn Williams and Ryan Jones is anyone's guess.
While Gatland has spent the last couple of days backpedalling faster than Chris Hoy in reverse gear – apparently, he was attempting to pay the Irish a "compliment" – his words will not be quickly forgotten. O'Driscoll, the outstanding back of the tournament in the way that Paul O'Connell has been the form tight forward, has been treating the subject as he would a bad smell, giving it a wide berth with his nose in the air. But the Ireland captain has had his squabbles with the Welsh before, not least with a certain Gavin Henson. It will be surprising indeed if he does not deem this week's events worthy of a mention come team-talk time.
"It's a long time since I've been coached by Warren, who is his own man," O'Driscoll commented yesterday. "I haven't picked up too many newspapers this week and I don't really have anything to say about it. I have no idea what he meant. You'll have to ask him. Anyway, words aren't worth a huge amount at the moment. There is no need to make the situation any bigger than it is, so we'll try to do our chatting during the game, right through the 80 minutes. Our sole focus is to win the game."
There was always a strong possibility that it would come to this: a Grand Slam match in Cardiff, that is, not a week's worth of fuss and bother about Celtic disharmony. Wales and Ireland are the best teams in Europe, and if there is a sense that O'Driscoll's men are in a marginally better place than their rivals, precious few travelling supporters expect this advantage to translate itself into a comfortable victory. As Clive Woodward discovered to his acute discomfort on more than one occasion during his stewardship of the England team, securing a Grand Slam against opposition who are really serious about not letting you have it is fraught with difficulty.
With the obvious exception of Italy, relatively new to the tournament and unlikely to go through the card this side of eternity, Ireland have waited for a Slam far longer than anyone. Since the turn of the century, it has been less a holy grail than a common or garden beer mug: France performed the feat in both 2002 and 2004, Wales in 2005 and 2008, England in 2003. Scotland have not managed it for almost 20 years now, but their spell of yearning is as nothing when set against Ireland's, whose one and only perfect run happened in 1948.
There are precisely no similarities between Karl Mullen's side of the immediate post-war years and O'Driscoll's team of today. How could there be? It is a different world now. Back then, there was a strong contingent of Ulstermen in the Ireland line-up; this evening, only Tommy Bowe and Stephen Ferris will start the game, and of those, Bowe now plays his club rugby in Wales. In '48, the presiding genius was the running outside-half Jackie Kyle. This evening, Ireland will look to O'Gara's right boot for succour and salvation.
For all that, ageing connoisseurs of back-row play might just be tempted to draw a misty-eyed comparison of sorts between the 1948 and 2009 vintages. The Grand Slam team possessed a loose unit of all the talents: the smash-'em-down tackler Bill McKay, the clever opportunist Jim McCarthy and the brilliant all-round athlete Des O'Brien.
This current combination is equally well balanced. Wallace, the open-side flanker, has been around a good while now and on his day, he can do everything better than everyone else. His partners, the destructive Stephen Ferris and the free-running Heaslip, are far less experienced, but equally striking in their contrasting ways.
Wales are no slouches in the loose-forward department themselves – there is no cleverer flanker than Williams, or more fearsome a straight-line runner than Andy Powell – but they will find the Irish trio devilishly difficult to subdue, especially if O'Connell bosses the tight exchanges with his customary authority.
Ireland's pack is high on confidence, having survived searching examinations by the French, the English and the Scots. As the prop Marcus Horan, a survivor of the last Grand Slam attempt in 2003, said yesterday: "We have more belief now. We're better equipped."
If Wales are to retain their title, they must win by 13 points or more – a mighty big ask. Ireland, on the other hand, can win by a gnat's crotchet and still go home delirious. The force is with them.