The entire Irish Cabinet travelled north across the border to the historic city of Armagh to inaugurate the new arrangements in the company of the new Northern Ireland executive, two dissenting Paisleyites excepted.
This was the first meeting of the north-south Northern Ireland Ministerial Council which was brought into being under the Good Friday Agreement. The new Council will oversee co-operation in almost every area of government activity.
Unionists present this as a sensible arrangement which will be of use in dealing with the day to day practicalities of administration. Nationalists and republicans, by contrast, see it as a means of drawing the two parts of Ireland closer together, and gradually reducing the significance of the border.
Another part of the new constitutional architecture is to be put in place on Friday with the first meetings of the British-Irish Council and the British-Irish Inter-Governmental Conference. This will provide a network to link London, Belfast, Dublin, Edinburgh and Cardiff.
The real significance of yesterday's meeting can only be appreciated in a historic context. The last attempt to set up such a north-south structure ended in chaos in 1974 when a widely-supported loyalist general strike brought Northern Ireland to a standstill and undermined the British government's authority.
Yesterday, by contrast, not a single protester braved the morning frost of Armagh while inside local council officers First Minister David Trimble - an active protester in 1974 - welcomed Dublin ministers with the words: "We have so much in common, so much that can bring us together, for our collective good."
He said the vast majority of Unionists had supported co-operation which did not undermine constitutional sovereignty, adding: "This recognises and provides for the dynamic and unique relationship between the people of the United Kingdom and the Republic of Ireland."
The Taoiseach, Bertie Ahern, said the days of conflict and division were over and that "today was unlike any other". He added: "It is unprecedented in my political career, in the political career of anyone else here, or in the political career of anyone who has ever served the people of this island. For the first time, elected ministers, drawn from both our great traditions and from both parts of the island, are gathered together in one room with a shared objective, to work for the common good of all the people."
Martin McGuinness of Sinn Fein described it as a truly historic occasion, expressing the hope that the new north-south institutions would eventually lead to the unification of Ireland. He added: "I think that today's development is an exciting, even joyous occasion. And hopefully, as far as we are concerned as Irish republicans that will see a culmination in the eventual unity of Ireland."