In June 1934, two lorry-loads of political activists, composed, as the Irish Independent put it, "largely of Protestants and Presbyterians drawn in the main from the . . . Orange districts of Belfast", made their way from Belfast to Bodenstown.
Radicalised by the strikes and social unrest of the Depression years, they had come to accept the challenge laid down by left-wing republicans: to transcend sectarian divisions and make common cause among the workers.
They carried banners proclaiming: "Wolfe Tone Commemoration 1934, Shankill Road Belfast Branch. Break The Connection With Capitalism."
Though the delegation was hardly representative of working-class Protestants in general, its very existence was remarkable. It seemed to suggest, however tentatively, that, in the words of the republican congress, "sectarianism burns out quickly where there is team work in common struggle".
What happened, of course, is that the Shankill Road workers were attacked at Bodenstown by the IRA, probably under the instructions of its then leader, Seán MacBride. Its members were kicked and punched as they tried to make their way towards Tone's grave, and the IRA heavies tried to seize their banners. The attack was motivated in part by a hatred of communism, but in part too by raw sectarianism.
At the moment when its official ideology - Catholics and Protestants making common cause - began to take on a tiny semblance of reality, so-called republicanism reverted to the basic instincts that lie behind its rhetoric.
While Orange bigotry has been open and obvious, the sectarian and ethnic hatred that lies behind much militant Irish nationalism almost never speaks its name. It takes the unbearable sight of Protestants walking the holy ground of republicanism - Bodenstown, the GPO - to unleash its feral tribalism.
The open display of sectarian rage on O'Connell Street on Saturday was ugly, frightening and shameful. But it was also salutary. Saturday was the perfect microcosm of a self-deluding State, steeped in complacency, suddenly confronted by a reality it has been determined to ignore. No one expected the obvious: that a march by Protestants asking the Republic's citizens to remember the IRA's crimes against their community, would be met by a visceral, violent loathing.
The organised assault on the marchers, and in their absence on the Garda, seemed to come out of the blue because the Republic itself has lapsed into deep denial of sectarianism.
Since the signing of the Belfast Agreement in 1998, the State has gradually reverted to the official ideology that prevailed before the Troubles. In the years of conflict, the Republic had to concede, however grudgingly, that there was a connection between the violence and official nationalism. The glorification of the gun, the simplification of history, the mythology of martyrdom, the denigration of non-violent struggle, the wilful ignorance of northern Protestantism, all came to be understood as having real consequences. Yet, almost as soon as the conflict ended, the State began to treat all of this stuff as if it were again inconsequential. A tribal identity could again be safely evoked for short-term political advantage. The bodies of dead IRA martyrs could be paraded through the streets.
The President could speak of the 1916 Rising, using the simplistic pieties of 1966. The Taoiseach could use a Fianna Fáil ardfheis to announce the re-instatement of the annual military parade to mark the Rising. It would be just a harmless political game.
We have the Green-fascist yobs, who literally wrapped the tricolour around them while they threw the bottles of urine at gardaí, to thank for showing what a stupid delusion this is.
Their rage at being denied the God-given right of oppressed Catholics to hurl paving stones at the heads of evil Prods is a rage at the very notion of historical complexity. In their own backyard, the Love Ulster organisers may not be too hot on the recognition of Catholic suffering, but their presence in Dublin was a useful warning against the perils of one-sided victimhood. The point of their march was simply to say that there was no monopoly on suffering in the Northern Ireland conflict, to act as a rebuke to the IRA's refusal to recognise that it engaged in a murderous oppression.
Their presence in Dublin was simply a way of saying that the history of the conflict cannot be reduced to propagandistic simplicities.
The thugs who set out to attack the march can't stand to have their own version of history complicated because they are dazzled by the most profound sectarianism of all: the refusal to recognise Protestants as legitimate historical actors. But the State, too, has been peddling historical simplicities in its efforts to make 1916 once again the badge of a tribal identity that supposedly underpins contemporary Ireland.
Let's remember that the Green fascists won on Saturday. They succeeded in their primary aim of stopping the march.
They grabbed some of the potent symbols of 1916 - the tricolour, fighting in O'Connell Street - and, for now, they hold them.