In a very real political sense, the British-Irish Council is meant to be Mr David Trimble's baby: the "British dimension" of a deal most celebrated for the creation of Northern Ireland's inclusive Executive, and a new network of North/South consultative and implementation bodies.
So it was perhaps ironic (if not entirely surprising) that it was the Taoiseach, Mr Ahern, who most conspicuously clasped that famous hand of history in describing yesterday's "unique" gathering in Lancaster House.
"Never before, perhaps, have representatives of all the peoples of these islands, and all our political traditions, come together in one room," he declared: "We include representatives from some of the oldest parliamentary institutions in the world, and also the youngest. And we come here in an atmosphere of friendship and mutual respect, to consider how best we can promote practical co-operation amongst us, for the benefit of all of our peoples."
Journalists have grown tired - perhaps even a touch embarrassed - by the constant invocation of "history" to describe the fast-flowing and unprecedented events in the few short weeks since the successful conclusion of the Mitchell review. But this was, without doubt, history once more in the making: "unique" certainly the presence under one roof of the leaders of the British and Irish governments; the First Minister of the Scottish Executive; the First Secretary of the National Assembly of Wales; the First and Deputy First Ministers of the Northern Ireland Executive; together with the Chief Minister of the Isle of Man government and the representatives of the States of Jersey and Guernsey.
Even by its very name, said Mr Ahern, the Council inaugurated yesterday - the final institutional structure prescribed by the Belfast Agreement - symbolised the "widening and multiplying" of relationships which have taken place alongside, and as a consequence of, the peace process.
For so many years the relations between the Irish and British, of necessity dominated by Northern Ireland, had been conducted in a bipolar framework between London and Dublin. "We were in the habit, inaccurately but revealingly, of thinking in terms of `Anglo-Irish' relations," said Mr Ahern. But that terminology was no longer adequate for "the complex reality" represented at Lancaster House yesterday.
Its genesis to be found in the 1981 Anglo-Irish Intergovernmental Council, the new council presented the opportunity to explore, at ministerial and official level, the potential for co-operation across the whole range of governmental activity. Said Mr Ahern: "The diversity which we represent can be a source of strength . . . But it also invests our relationships with a degree of complexity which we will have to respect if we are to make a long-term success of this new institution." And he continued: "No two of us are exactly equivalent in political jurisdiction, and there are wide divergences of scale and resources between us. We must respect each other's circumstances, and accept - as a positive rather than a negative factor - that not all of us will wish to engage in all of the activities taking place in the framework of the council."
This may have struck a somewhat jarring note with the listening Ulster Unionist Party delegation - reminding them that the British Irish-Council is not, in fact, Dublin's top priority, and that conflicting political purposes lie at the very heart of the new dispensation.
However, the Government cannot be accused of reticence or lack of interest in this most novel of all the new arrangements. For, as the Taoiseach reminded everyone yesterday, his Government responded immediately to the devolution referendum results by opening Consulates-General in both Cardiff and Edinburgh.
Indisputably Dublin's prior and over-arching concern will be to develop the dynamic executive and harmonising potential of the new cross-Border bodies. However, if unionists are worried about an over-emphasis on "cross-Bordery", the reality would appear to be that in the matter of "British-Irishry" Dublin is also ahead of the game.
It is true Mr Trimble and his still small circle have been consumed by the internal unionist battle. In fairness, too, their thinking on the east-west dimension, and its potential, extends far beyond the media focus on the notion that the English might share some of the games should they again host the World Cup.
However - quite apart from Dublin's already high-profile diplomacy in Edinburgh and Cardiff - Mr Trimble must know that, in Mr Blair's devolved Britain, he cannot readily assume automatic convergence around any common "British" interest. The challenge for the UUP leader will be to dispel suspicions that the British-Irish Council will be little more than a talking shop - a unionist comfort zone while the real focus and energy lies with the North-South Ministerial Council.
One early indicator of the seriousness of this endeavour would be a decision by the Northern Ireland Executive to establish its own offices in Edinburgh and Cardiff, and in London. But already there is speculation that if Mr Trimble's real concern is to consolidate the Union and Northern Ireland's activities within it, his greater interest might ultimately lie with the Joint Ministerial Council through which Whitehall will liaise with the devolved parliament and assemblies of the UK. But that is for the future. For the moment history-a-plenty has been made. The "deepening" and "widening" so often quoted in relation to Europe comes readily to mind in the context of the increased diversity and complexity of the relationships now unfolding within these islands. If they are allowed to take root, none can say where they may or may not lead.
But the flowering of these new relationships will depend on the ability and determination of all sides - and ultimately, in particular, of the two governments - to resolve now the most complex, difficult and resistant issue of all. For all the joy and celebration, hope and expectation attendant at the dramatic and groundbreaking events of the past three weeks, decommissioning still casts its shadow over Northern Ireland's bright new dawn.