Their stories both begin in 1899 but it is only now that history deigns to bring them together.
For Shamrock Rovers and AC Milan, who clash in Europe's secondary competition in Tallaght this Thursday, were both founded in the final year of the 19th century.
Of course, some Rovers faithful will quibble about that particular historic moment, although sadly they won't get a chance to do so in the '1899 bar' in Tallaght next Thursday as empty stands mark yet another stellar moment in the club's modern history.
Some claim that 1901 marks the date of foundation, in Ringsend's Shamrock Avenue, from which they earned their name; indeed a plaque there commemorates the supposed historic occasion.
Others, though, insist the club was founded in 1899, the same year that three English butchers began a football club to which they attached the English sobriquet, Milan, rather than the native Milano.
The Kilcoynes, former owners of the club, inscribed 1899 as the date of foundation on the gates of Milltown; the latterly spiritual home of the club for 65 years from 1922 to 1987, abandoned in the 1980s during one of the club's occasional upheavals. Understandably, many quibble with a Kilcoyne version of history.
A Ringsend fisherman, Larry Fitzpatrick, is sometimes credited as being a founder member - again, there is conjecture, with Lar Byrne also name-checked.
Tradesmen certainly founded AC Milan, three butchers in fact, Alfred Edwards, Herbert Kilpin and Samuel Davies.
Within a year they had won their first title, backboned by English lace workers enrolled in the winter of 1899 in Milan's Fiaschetteria Toscana bar.
Rovers' early history was more fitful but, after several false starts, they entered the FAI Cup in 1921 as a Leinster Senior League outfit, losing in the final, but they would later historically amend that result by becoming the Cup kings of Irish soccer.
In the following season, the club won the League of Ireland title at the first attempt, going 21 games unbeaten and scoring 77 goals.
By the end of the club's fifth season in the league, Rovers had won three league titles and one cup as they began to establish their credentials as Irish footballing royalty.
By 1949, Rovers had established themselves as Ireland's most successful football club, winning 44 major trophies - six titles and 11 Cups highlighting an avaricious trophy haul which numbered 27 other Cup wins in minor competitions.
Milan - Inter Milan would come later, but AC Milan would always be simply Milan, perhaps just as Shamrock Rovers are simply Rovers - would hungrily gather titles too, headlined by 18 Scudettos and seven European Cups/Champions Leagues.
Unlike Rovers, though, Milan are not the most successful club in their country, an honour bestowed upon the Old Lady of Turin, Juventus.
But they still endure as one of the most celebrated names in world football, as synonymous with Italy as Rovers are with Ireland.
It remains an oddity, however, that for all their respective dominations, and indeed given the nature of European club competitions since their foundation, meetings between Italian and Irish clubs have been decidedly rare.
It is less than a decade since Juventus and Shamrock Rovers met in the third round of Uefa Cup qualification, but before that Irish clubs only encountered Italian opposition twice, Limerick against Torino in the first round of the old Cup Winners' Cup in 1971 and, famously, Athlone Town, who welcomed AC Milan to a muddy St Mel's Park in 1975.
"The biggest thing to happen here since the Earl of Lucan burned down the bridge here in the 17th century," said the International Herald Tribune with no little restraint.
The 45th anniversary of that encounter is approaching, a 0-0 draw which could have been so much better for the Midlanders had John Minnock not missed a 30th-minute penalty kick, before the reverse fixture ended 3-0 in the San Siro in favour of the Italians.
Athlone had only just recently rejoined the League of Ireland in 1969 - that same year, Milan conquered Europe again - after a 41-year absence, but almost stunned their exalted rivals.
Milan's Nereo Rocco stated before the game that "Athlone's players may only be part-time professionals but I shall be happy enough to go home with a scoreless draw".
After the procession of a pipe band, and a goat, that aptly preceded the remarkable confluence of princes and paupers, he was more than happy, mightily relived in fact, after Enrico Albertosi saved Minnock's effort, although he had benefited from clever scouting.
Three days earlier, Minnock had scored from the spot against Cork Hibs in a league game, watched by a covert spy. "Bottom left corner", he inked in his diary. "I was looking at the 'keeper Albertosi, he was looking at me," Minnock later told RTÉ. "I was looking to my right but putting it to my left. He dived and saved it. I didn't hit it hard
"I was just placing it. Some supporters didn't let you forget about it - if we got a penalty they'd shout, 'Keep Minno away from it'!"
Athlone retained admirable hope ahead of the return after their stout effort. "We should have won," said manager Amby Fogarty, "but I am happy with a draw."
Giovanni Trapattoni was embarking on his first coaching venture with the Milanese, alongside Cesare Maldini.
It may be an apocryphal memory that recalled Trapattoni's exclamation, as his Gucci shoes splattered in mud upon arrival - "Is this some mistake?" - but he was more charitable when later remembering the encounter when managing Ireland.
Indeed, he returned to the midlands in 2011, meeting Minnock amongst others, and reflected on a "beautiful experience".
"I want to give my regards to this city. 36 years ago, I played in this beautiful, little town. It's a pleasure to be back.
"I remember it well. The spectators were near the line, very close along the pitch. I remember that even though it was many, many years ago. The day was a beautiful experience."
Thursday will be unique; for one thing, a one-off tie, and also behind closed doors too, far from the glamour of the San Siro or the Stadio Braglia in Modena - U2 were playing in Juve's habitual home that night - where Alessandro Del Piero's stunning free-kick downed Rovers nine years ago.
Milan have defensive issues, but the signings of Brahim Diaz from Real Madrid and Brescia's Sandro Tonali have introduced youthful exuberance to a side rebuilding under Stefano Pioli.
Enda Stevens, now an established Irish international, featured in both games. And although Rovers may count the cost in missing TV rights due to Covid, a sporting win could be invaluable.
"There's always a chance and Rovers play a nice way of football and I think they can cause a lot of problems to AC Milan," Stevens said. "I think Milan will be a bit surprised and hopefully they can make a game of it."
Tallaght may not resemble the muddy midlands when Zlatan Ibrahmovic & Co sashay into town this week, but the magnitude of the occasion will be no less dimmed, nor the potential ramifications should a famous upset be recorded.
And 121 years since they began their respective existences, this is a contest of the ages.