Funny thing. My grandfather grew up in the first decades of this century and the heroes of his youth are as remote now as the places he lived and played in. Jones' Road was what he called Croke Park and he remembered running on it when cinder track surrounded the scutch grass.

Sport was young back then. He knew football, but the men whose names lingered in his memory are gone too now. The St Laurence O'Toole's parish in Seville Place sent out tough teams from three different clubs, none of them better than the O'Toole's sides back-boned by various Synotts and McDonnells. They were local heroes. Big men, golden in their prime, quietly confident that they were the best of their generation.

That was then. Sport regenerates itself as relentlessly as a big city. When we come to the silly business of picking teams of the century nobody was left to speak for Josie Synott and the boys.

Even the best of men wither and the toughest of mountains succumb and the greatest of buildings come down. The earliest generations of men and women to excel at organised sport got their last headlines on their tombstones long ago. That was their lot.

So isn't it humbling for us to be scrabbling on to the foothills of a new century, to be gazing up at a new, unconquered millennium? Mortality is a back-pack full of stones. We won't make it too far.

The marks we set will be easily surpassed and the heroes we make will be sepia-coloured and frayed by the time the world completes another lap. None of our kings and queens of sport will be on all-century lists in 2099. Our stadiums will be rubble, our memories washed away, our arguments, rivalries and passions trivialised by the decades.

In a hundred years somebody will sit down to review a century of sport. We will be the merest flecks in the rear view mirror. We will look small when held up for comparison with the new, new thing. The records we set will be quaint and dusty, the people we cheered will be innocent and staid. They will peer out from photos and videos, frozen forever with their odd haircuts and coarse uniforms. Our enthusiasm will be strange and curious antiquities and the life we breathed into our sport will be long gone.

Sport is a marriage of time and context. We will have no way of conveying to our great grandchildren the furious majesty of Brian Lohan, the granite hardness of Roy Keane, the fluid beauty of Sonia O'Sullivan. Muhammad Ali's firm but gentle hold on our imagination will be incomprehensible. Michael Jordan's supernatural powers will be a dead grandfather's lame reminiscences.

We have one distinction. Organised sport has grown up with this century of ours and for this moment at least we can stand on a summit of time, take a deep breath and study the long road behind us.

We are the first to do it. We are capping off a century that has brought sport from inter-village rivalry to global obsession, from past-time to business. We have changed the quality of our leisure time and so changed our lives and imaginations.

Perspective is skewed from the point where we stand of course. Those landmarks we passed last, they loom largest. Ali is the defining sports-person of the century because he changed utterly that part of the century which we know. He amounted to more than sports people can aspire to be. Sport was his medium, not the outer limit of his possibilities. He was about race and politics and beauty and poetry, too. There was a time back before Jesse Owens when we couldn't imagine sport being like that.

Between times, Ali boxed as well. You can argue the case for better heavyweights, more powerful heavyweights, more classical heavyweights, but you cannot find anything in sport to match the huge courageous daring of the man who reclined on the ropes in Kinshasa and let the greatest ogre of the age blow himself to a standstill. George Foreman was dismantled like a man kissed by death. Sonny Liston had known the same experience.

While you argue you will not produce anything to match Ali's defeat of Frazier in Manilla. I watched it recently. There has never been a more brutally draining struggle between two men. They fought each other to the brink of ruin and beyond the definition of bravery.

"Lord I hit him with punches that would bring down the walls of a city," said Joe Frazier afterwards. Joe was broken then, but he had no right to be. Boxing should have finished at that point. Taken a bow and said goodbye.

Boxing, which now is nothing but sadness, was special for the longest time. For us it is a means by which we can trace our progress as an emigrant tribe. Count the rungs from the bottom floor. At the turn of the century the world of boxing was filled with Irish names. An era book-ended by two men called Jack Dempsey. The nonpareil from Kildare (real name John Kelly) was full of the raw romance of the time. He had 41 pro fights before his infamous 45-rounder with Johnny Reagan in a bout that had to be moved from Long Island after four rounds as the ring flooded with rain. The fight finished in a snow blizzard. Dempsey died young, just 33 when he shuffled off this mortal coil not long after a losing fight with Tommy Ryan.

And then, with the century newly minted, came Jack Dempsey, the Manassa Mauler. He would be the irresistible high point of the early decades. What we know about sports promotion started back then when Tex Rickard began flogging Dempsey's legend. The first $1 million gate. The first $2 million gate. In Chicago, old timers still genuflect when they pass Soldier Field where Tunney beat Dempsey. That fight ended the era which it defined. Wall Street would fall through the floor not long afterwards. The Irish would leave the stage to the Italians, the blacks, the Hispanics.

Boxing is no longer the index for us, but sport will always be an escape route. Dempsey came out of the mines. The future of Irish soccer will come out of Tallaght. Maybe 90 per cent of what came in between came out of the working class. There is a democratic beauty in that, there in one world where sheer hunger and hard work are rewarded.

It was always easier of course to make a million bucks with a big character than it was with a great team. Despite what we tell ourselves, we are besotted by the cult of the individual. How many teams from the first 50 years of the century dally in our memory now?

The four-in-a-row footballers of Wexford? The Cork hurlers of the 40s? The bent Chicago White Sox of 1919? Accrington Stanley?

There are few things lovelier than seeing human beings acting in harmony in extremis. JBM pulling on Fenton's head-high ball. Pele and Jairzinho dissecting the Italians of 1970. The old baseball double play infield of Tinker to Evers to Chance. A steaming, breathing Welsh pack birthing a ball on a muddy field with some scrum-half imp from the mines acting as midwife.

In the end, though, the individual wins out. The lesson of sport is like the lesson of life. We are alone. Pele above Santos, Ring above Cork, Ruth above the Yankees. David over whoever he was playing for when he beat Goliath. That's what lasts.

It is a commonplace now to denounce sport as the new religion, the fresh opiate of choice for the masses. What if it is? Less blood is spilled over sport than over creed, and, if people need endless diversion and refuge, it is not the place of sport to fix the world from which they flee.

The attraction is obvious. Apart from war, sport is the last arena of immediacy. You don't take a rain-check. You don't ring a friend or ask the audience. You don't fetch a doctor's note. You step up and kick the last-minute penalty. You take the punch. You are Michael Jordan in the last game of your life, a championship on the line, your team behind, and you let the clock run down till you execute and then swoosh. Where else do you get that adrenaline, that spontaneity?