Following the recent decision of Sinn Fein, the IRA's political wing, to support the police in Northern Ireland for the first time, Kevin Connolly reflects on the dark days when Britain fought the IRA to keep Ireland within its empire.
There is a cold hour just before dawn, when the light is the colour of lead, when the past seems a little closer and a lot more real than it does in the clearer light that comes later in the day.
The familiar signs of modern life have yet to seep back into the streets: the cars and buses, the tourists with iPods and the busy pedestrians with places to be.
Dublin is still a city of graceful Georgian terraces and, at this time of day, the scrubbed-pale stone staircases that sweep up from the street to the imposing front doors look just as they must have looked around this time in the last century.
To complete the illusion, the only sign of movement on the chilly landscape came from the frock-coated doorman of my hotel who is dressed, as is the way of it in such places, like a Hapsburg Dragoons officer.
I alone, heading for the Sinn Fein conference centre, struck a jarringly contemporary note, swaddled against the early morning cold in cheap, lumpy layers of fleece, like a scarecrow whose run of financial good fortune has come to an end.
There is a good chance I suppose that the morning of 21 November 1920 (the first "Bloody Sunday") dawned in the same atmosphere of chilly damp - winter days in Dublin often do.
On that day, IRA gunmen burst into a string of houses that lay along my route to the conference centre and shot dead 14 British officers and intelligence officials.
In 1919 the IRA became the army of a unilaterally declared Irish Republic
The Ireland of those days was inured to brutality on all sides but there was something about these killings that shocked the Dublin public.
Maybe it was the curiously pathetic fact that most of the victims were dragged from their beds and shot in their pyjamas. More likely it was the story of how the pregnant wife of one of the officers had thrown herself on top of his wounded body in a vain attempt to save him.
She gave birth to a stillborn child a few days later.
It disclosed something of the underlying truth of guerrilla warfare too. Some of the IRA gunmen were efficient and ruthless, others were too nervous to hit their intended targets with dozens of bullets fired inside a bedroom.
The killings were a shock to the British establishment too.
Some of the victims were given a state funeral back in London at which both Lloyd George and Winston Churchill followed the coffins.
They appear to have had less of an impact on some of the British officers actually serving in Ireland.
General FP Crozier, having helped direct clearing-up operations, went back to barracks, had a game of squash and a bath, and then took himself off to lunch, apparently in good spirits despite all the slaughter.
And of course, the slaughter was not done.
Britain had recruited two separate paramilitary forces in an attempt to crush the Irish rebellion: the Black And Tans and the Auxiliaries.
A scene from rare film footage of the 1916 Easter Rising
Their ostensible role was to support the officers of the Royal Irish Constabulary, mainly Catholic Irishmen of whom hundreds were to be murdered by the IRA.
The real role of Britain's irregular forces was to meet murder with murder, or at least with violent reprisal.
A few hours after the British officials were killed, troops and police officers opened fire on the crowd at a Gaelic football match in Croke Park, on the Northside of Dublin.
A further 14 people, some of them children, were killed.
And the point of all this? Well, the part of Dublin in which I found myself on that Sunday morning - which once witnessed a terrifying step down the road to violence - was witnessing an important step towards peace.
And in the same way, Croke Park - once the scene of one of the most disgraceful acts in this long and tortured story - is itself about to provide another little reminder of how hopeful are the times in which we live in Ireland now.
Croke Park is the home of the Gaelic Athletic Association
While the national home of Irish rugby is refurbished, football and rugby - long derided by lovers of Gaelic sport as English-imposed "garrison games" - are to be played at Croke Park.
By chance, the English rugby team will be among the first visitors, and the incongruous sound of God Save The Queen will echo around a huge stadium which includes a terrace originally built from the rubble of Dublin buildings destroyed by British shelling in 1916.
If you happen to catch the game, there is a name to listen out for in the commentary.
Not one of the players on the pitch, but a young man called Michael Hogan, who was the Tipperary captain in the game being played on 21 November 1920.
He was shot and killed on the field of play and one of the stands at Croke Park still bears his name.
That name - like the names of the graceful streets through which I walked to the Sinn Fein conference on my more recent Sunday morning - are reminders of how Ireland, as well as things between Ireland and Britain are turning out in a way that no-one who was alive in November 1920 could have dared to hope.
There was still a lot of suffering to go, of course, on both sides when the events of that first Irish "Bloody Sunday" were done and much of it reaches into our present day but sometimes it is worth daring to reflect on how much things have changed here, and changed for the better.
From Our Own Correspondent was broadcast on Saturday, 3 February, 2007 at 1130 GMT on BBC Radio 4. Please check the programme schedules for World Service transmission times.