'If you're looking for a real lift-off point for our European quest, it has to be beating Saracens at Vicarage Road on Sunday, November 28, 1999.'
Anthony Foley, 'Axel – A Memoir'.
Or, indeed, defining occasions.
Theirs is not an enduring rivalry but their brief encounters have always been deeply meaningful, from the initial demonstration of Munster's flowering greatness, through their eventual confirmation as European giants and, now, perhaps, their re-emergence as realistic contenders at the top table.
While many Munster supporters rightly identify their maiden win in France as the key stepping stone in their emergence as perennial European contenders, their first victory on English soil was arguably even more influential.
During that 1999/2000 season, beating an ageing Colomiers was one thing. But dispatching the highly vaunted Saracens in a thrilling Vicarage Road clash was a much more meaningful illustration of their hardened resolve.
As Irish professional rugby lurched uncertainly into a new, post-Lens millennium, Munster had repatriated Keith Wood from England, as well as signing Mike Mullins and Australian second-row John Langford.
The English clubs had been reintegrated to European competition after a familiar exercise in tossing their soothers from the pram had led to their withdrawal a year earlier.
In the guise of Saracens, Munster were presented with undeniably stiff opposition – the Londoners were backboned by French genius Thierry Lacroix and South Africa's Francois Pienaar.
Munster had lost on their only previous visit to England – against Harlequins a couple of years earlier. But a win in Ulster for the first time in 19 years had energised a province seeking to push aside the collective national despair visited upon many of their number by Argentina at the World Cup in Lens.
Declan Kidney was coach and, anticipating the circus atmosphere that the glitzy Saracens side would parade in Watford, he instigated one of the most famous pieces of his psychological repertoire.
The Londoners, aside from raucous Fez-wearing dancing cheerleaders and such, used a motorised car to wheel out the kicking tee for home place-kickers.
During a video session in Limerick directed by Niall O'Donovan, the squad's attention was interrupted when Kidney paused the tape, donned a Fez, Tommy Cooper style, and began operating a remote-controlled car.
"Let's just say I covered the cheerleading angle as well," Kidney would joke later.
When he asked the squad to tell him what had been happening on the video before he stopped it, there came no answer. They absorbed the lesson. Just.
"Before this game, people came to Thomond Park to watch these big European sides," said Munster's current forwards coach O'Donovan, then assistant to Kidney, in Ciaran Cronin's 'Beyond Our Wildest Dreams'. "After beating Saracens, people started to come to watch us."
A week later, Munster won away in France, skimming past another significant psychological milestone in their European development. The return clash in Thomond was a classic and the terraces swayed to the pulsating rhythm of a contest that deviated wildly from one side to the other.
Ultimately Munster, once more, thieved a late win.
Even though they repelled Toulouse in a remarkable semi-final that season, Northampton ultimately undid them in a grim decider but the Irish province had truly announced themselves on the European stage.
It would take almost a decade before the sides clashed once more; by this time, Munster were defined by their European excellence while Saracens had comparatively retreated into the shadows.
When they clashed at the penultimate stage of the 2008 campaign, the Irish side, again under Kidney, were chasing a second title in three seasons while the English combo, under Alan Gaffney, were still to embark upon their 'South African' project.
Richard Hill, England's World Cup-winning flanker, was the sole survivor from the previous epics between the sides; this clash in Coventry eerily resembled the city of its staging, brutally austere and drab to the outsider.
Within the Ricoh Arena, the action was never less than compelling. Saracens led early on but Munster assumed control until a late surge from the home side, with Hill central to the late drama as referee Nigel Owens whistled for a penalty which seemed harsh to many observers.
"I don't need to spend the rest of my life reviewing a video," a rueful Hill said a year later. "You appreciate the magnitude of what you were involved in but... it's not going to change anything, is it?"
Munster would move on to claim their second Heineken Cup title in three years, announcing themselves as monarchs of Europe; since then, their status has been eclipsed.
Last Saturday was only the fourth meeting between these sides and all have freighted deeper implications for the winners, which have until now always been wearing red.
The Englishmen believe they have more room for improvement this weekend as the fixture returns to the partially condemned old ground in Watford; whether Munster can add more to their game remains to be seen.
One thing is certain, however. Munster may have won four from four but history and statistics – the aggregate margin of victory is just 10 points – informs all of us that doubt about the outcome will linger until the very last whistle.