They made history again last night.
For sure, there was none of the sweet magical sensation which greeted the Belfast Agreement in the sleep-starved early morning hours of Good Friday, 19 months ago.
The road from there to here had been long and hard, the process more akin to trench warfare than peace-making. And the knowledge of the journey still to come made understandable enough the lack of euphoria, the lack, almost, of any sense of occasion. But it was history in the making for all that.
The Democratic Unionists gave early reminder of their mastery of the procedural wrangle. They would not be complicit in what Peter Robinson termed the "chicanery" of the device to reinstate Seamus Mallon as Deputy First Minister designate without the need for an election as prescribed by the original rules.
Hoping, perhaps, to tempt Mr Mallon, the DUP deputy leader taunted him as a putative "minister for loopholes" even "a minister by the back door."
Mr Mallon quietly endured. As did the Ulster Unionists, when Mr Robert McCartney explained the reason for the invitation to Mr Mallon to resume his post as "cover for the unelectable - because Mr Trimble today was unelectable."
And there were some heads hanging low and eyes not met a while later, when the DUP insisted on literally standing up to be counted in support of their motion to exclude Sinn Fein from office - and disdainfully inviting Mr Trimble's dissident colleagues to join them.
None did. In the immediate aftermath of Saturday's Ulster Unionist Council decision it had become clear that none of Mr Trimble's antis would be providing the necessary 30th signature with which Dr Paisley and Mr Robinson might torment their leader.
"Why would I," demanded one, "sign their motion and sit back while they kick us all over the place, only then to watch Peter Robinson and Nigel Dodds walk into the Executive?"
The shadow of decommissioning hung over the proceedings. Which perhaps explained a certain reticence on Mr Adams's part when he described the Mitchell review as "a watershed opportunity." The Sinn Fein president allowed himself some optimism, but it was tinged with caution.
"The rejectionists have until now had their day," he declared, "But the beginning of the end of all that can come here."
Monica McWilliams was more determinedly upbeat. Having heard Cedric Wilson's rallying cry for the "David and Goliath" struggle against this "betrayal", the Women's Coalition leader expressed the hope that "the politics of self-righteousness, when God is all on your side, is coming to an end."
For Seamus Mallon this "landmark day" did mark the end: the end of a 30-year battle by him, and his party, to bring powersharing about. Seated beside him his party leader, Mr John Hume - recovering from illness and watched from the gallery by his wife Pat - can only have savoured the moment when his dream became reality.
And as the reality struck home, in an instant hesitation was gone, doubt dispelled. Those watching knew it. For all that they had been here before. For all the natural distrust of rhetoric, and the certainty of the uncertainty ahead. This was history. For how else to describe the moment, just before the clock struck 6p.m., when Mr Adams nominated Mr Martin McGuinness to be Northern Ireland's new Minister of Education?
The Initial Presiding Officer, Lord Alderdice (not yet confirmed in his post), seemed to go on at interminable length describing the operation of the D'Hondt procedure. At 5.38p.m. we were ready for the main event.
But, true to form, Dr Paisley raised a (mercifully brief) point of order. At 5.41p.m. Mr Trimble nominated Sir Reg Empey to the top post in charge of Enterprise, Trade and Investment. Mr Hume quickly followed, nominating Mark Durkan for Finance and Personnel.
Dr Paisley had the chance actually to take Education, but Mr Robinson's choice was for Regional Development.
Yet it was only when Mr McGuinness claimed his prize that the ambition of this endeavour - the construction of this extraordinary coalition - really sank in.
It was too much for Mr Wilson, the leader of the Northern Ireland Unionist Party. "I can't sit through this obscenity," he declared with feeling; "I'm leaving."
Mr McCartney sat with his head in his hands, his face a tale of deep, bitter distaste. The sole UKUP member would have liked nothing better than to have stormed out, taking the bulk of outraged unionism with him, never to return.
Nor would he have found much comfort in the assertions of Mr Robinson, and later Mr Dodds, that they were accepting nomination to office in order to "frustrate and thwart Northern Ireland being conveyed into a united Ireland." Mr McCartney knows about ground conceded never to be recovered.
Of course, there might yet be a turning back. Much is made of the purr of the waiting ministerial cars, the lure and aggrandisement of office. But this is overly cynical. And, while it might characterise the motivation of some individuals, it will not be the basis on which unionism's final dispositions are made.
It also remains to be seen how Mr Robinson and Mr Dodds will play their promised role as "ministers in opposition" - and for how long this system can tolerate them in the Executive but not at the Executive table.
We should not, however, expect Mr Trimble and Mr Mallon to be in any rush to remove them. Moreover, it is clear that "the battle for the soul of unionism" which matters is not between the DUP and the UUP, but that still being fought within Mr Trimble's own ranks.
Some of the more publicly vocal doubters may well have looked shame-faced yesterday, as the DUP put them to the test. But others found voice to cry "Hypocrite" as Mr Robinson rehearsed his own terms for taking office.
And there is within the Ulster Unionist Party, on all sides, a real and deep-seated feeling that they have had to endure the pain of the attempt to negotiate a future for Northern Ireland, while ambitious men within the DUP hope to experience the gain.
In crude terms, there is no disposition there to take lectures from the DUP. That said, there is a growing disposition within the UUP to bring the whole edifice down if the IRA does not deliver on decommissioning.
Sir Reg Empey emerged before the waiting cameras to declare: "The twin issues of devolution and decommissioning haven't gone away, you know." For the pessimists it was a reminder of how drastically the whole thing can still go wrong. For the optimists, it was simply a challenge to see still more history made.