How the IRA of 1918-21 bought, captured or stole the weapon will never be known. But it had passed into the hands of an Irish family and remained with them throughout the subsequent war in which Michael Collins died for the Provisional government of the Irish Free State, and at the end of which Eamon de Valera surrendered on behalf of the anti-treaty Republican forces. And when that war was over, like thousands of Irish men and women, the Carlow family had kept their Lee Enfield rifle, just in case. In case the British returned. In case the Irish civil war was not really over. In case the Irish ceasefire did not last.
Now, of course, the old Lee Enfield was an antique, the cause of humour over dinner a few hours after I found it. Maybe, someone suggested, it should be given to a local museum. But I could not help remembering that gun when I heard that US Senator George Mitchell was going to look into that most sinister of all stumbling blocks in the Irish "peace process": the "decommissioning of weapons". For the ghosts of Irish history haunt the present more palpably than most of us imagine and, by and large, civil war participants do not usually give up their weapons when they lay down their arms for a ceasefire. They keep them for protection until peace treaties are signed.
Indeed, back in December of 1920, when Collins was waging his first war - against the British - he blamed Lloyd George's insistence on "decommissioning" for continuing the bloodshed. "... although terms of Truce were virtually agreed upon", he wrote, just before his death in 1922, "they were abandoned because the British leaders thought those actions indicated weakness, and they consequently decided to insist upon surrender of our arms. The result was the continuance of the struggle. British aggression went on unabated and our defence was kept up to the best of our ability".
Mitchell may not know that when the Irish civil war ended in 1923, de Valera - as he is quoted in Tim Pat Coogan's biography - tried to secure "suitable buildings" in each province of Ireland "to be used by [Republican forces] as barracks and arsenals, where Republican arms should be stored, sealed up and defended by a specially pledged (sic) Republican guard". After elections, the arms could be reissued, de Valera thought, "in such [a] manner as may secure the consent of the government then elected". In 1923, the Irish government insisted all arms must be surrendered and a few token "heavy weapons" - or what passed for field guns in the rag- tag army of the anti-treaty men - were given up. But the rest were dug into the earth, hidden in roofs or cow-byres, where many of them remain to this day.
Ministers in the present-day Irish government have been both infuriated and fearful of John Major's repeated insistence on "decommissioning" as the price for all-party talks that included Sinn Fein - not just because of the terrible but private and unpublicised warnings of attacks into the Republic which the Protestant paramilitaries promised the Irish cabinet if the Belfast ceasefire broke down, but because, historically, the men and women of Ireland do not hand over their guns. Even after the 1798 rising, Irishmen hid their pikes rather than surrender them to the English.
Would an Irish peace really be in danger if the IRA and the so-called "loyalists" buried their guns in the garden? The Lebanese civil war suggests it would not. When the Christians and Muslims of Beirut ended their conflict in 1990 - after the Syrian bombing of a Lebanese rebel general's last redoubt - there was an ostentatious call by the new Lebanese government for the handing over of all militia arms.
A few trucks were ceremonially given to the newly reconstituted Lebanese army and a boatload of rocket-propelled grenades was dispatched to Croatia by the greediest of the Christian militiamen, but most of the Kalashnikovs and pistols and grenades and ammunition boxes were buried in the hills or beneath the floorboards of Lebanese homes.
Senator Mitchell - who, ironically, is of Lebanese as well as Irish extraction - might take note of all this. For I know hundreds of Lebanese families who have kept their guns; in my small area of west Beirut they are mostly hidden in cupboards, with the tacit permission of the security forces. The deal is simple, though unwritten: if the peace continues, the guns will never be used; but if the army cannot keep the peace, then the guns become once more the ultimate means of each family's defence. So the price a government pays to keep the guns out of sight is the success of the security it provides for its own people.
Of course, there are terrible risks. Once Tito had satisfied his thirst for revenge against the wartime Croats, he insisted that every family in Yugoslavia keep a gun in their home for defence against invasion. And when the southern Slav civil war broke out in 1991, those same guns were pulled out of cupboards and attics and used to terrible effect. But it was the fragmentation of Yugoslavia and the nationalist ambitions of its little dictators that fuelled the new war - not the guns. Besides, most of the Bosnian warlords were, by 1992, breaching the arms embargo by supplying their men with newer weapons.
An international commission may decide that the IRA must make some token gifts of hand-held missiles to neutral parties - stored, perhaps, in one of de Valera's "suitable buildings", along with some Protestant ammunition. And, given that phrase in the official communique about "all arms" being "removed from Irish politics" - shrewdly spotted yesterday by Sean Cronin, the veteran Irish Times Washington correspondent - we might expect a modest gift of rifles, too, from the Royal Ulster Constabulary.
In reality, however, Major and John Bruton may well decide that the garden - where many an English Civil War brassard lay hidden over the centuries - is the best place for the IRA's armoury, a place where it can rust and congeal into history. After all, those English Civil War swords that survived Cromwell now decorate the walls of many a Home County pub - just as 18th-century pikes can occasionally be found above the fireplaces of Co Cork bars. One day another generation may even see the occasional Kalashnikov hanging above the hearth - well rusted, of course. There could not be a more powerful symbol of peace.