It was a hard-fought action worthy of the Alamo and other last stands of military history. On Easter Monday 1916, Sean Heuston led the D company of the First Battalion of Irish Volunteers to seize the Mendicity Institution on the south of the Liffey at Usher's Island.
His orders from James Connolly were to engage any British troops coming out of the Royal Barracks, long enough to give Commandant Ned Daly time to build his defences at the Four Courts. This mission was expected to take only a few hours, after which Heuston could withdraw. In the event, he held the building for over two days.
The Mendicity was then, as it is now, a charity set up to feed Dublin's poor and homeless, but both staff and the unfortunates who awaited their only square meal of that day were unceremoniously evacuated at gunpoint while Heuston and his men barricaded the doors and smashed windows to take up their positions.
After they fired their first rifle volley against British troops advancing along the North Quays, their opponents fell back and Heuston decided to hold his position.
"The British command soon realised that this small unit posed a serious threat and surrounded the building," says Declan Costello, whose grandfather Patrick Kelly was among 13 Swords Volunteers sent as reinforcements the next day.
"It was a tiny garrison of only about 30 men fighting up to 400 Dublin Fusiliers who, as they closed in, started hurling in hand grenades.
"Imagine their surprise when the Irish rebels caught them and threw them back out!"
At least two of the rebels, Liam Staines and Dick Balfe, were seriously injured when the bombs exploded before they had a chance to throw them out the window. With no food and hopelessly outnumbered by forces equipped with superior ammunition, Heuston surrendered on Wednesday.
"My grandfather was taken to Arbour Hill and court-martialled on May 4 along with his fellow combatants," says Declan.
"He was sentenced to death, but this was later commuted to penal servitude. As we know, Sean Heuston was executed on May 8, but Patrick and the others were taken to Arbour Hill and Mountjoy, and later transferred to Dartmoor, Maidstone, Lewis and Pentonville.
"They were moved from prison to prison, because they caused trouble. They considered themselves prisoners of war and looked for basic human rights, which they didn't get, so they went on hunger strike.
"Having shared jail time with Eamon de Valera and Thomas Ashe, Patrick was released in June 1917, and he smuggled out a poem written by Ashe, which reads:
'Let me carry your Cross for Ireland, Lord, For Ireland weak with tears,
For the aged man of the clouded brow, And the child of tender years;
For the empty homes of her golden plains, For the hopes of her future too,
Let me carry your Cross for Ireland, Lord, For the cause of Roisin Dubh.'
Patrick Kelly married and had six children. He bought a piece of land in Lusk, Co Dublin, and built a house, a bicycle shop, sweet shop and electrical repair shop.
"He was the first man in the town to have a radio. He'd built it himself and whenever there was an All-Ireland match, he hung a loudspeaker outside the shop and hundreds of men from the Naul, Balbriggan, Donabate and other towns nearby gathered in the square listening to it," says Declan.
Like most of his generation, he shared nothing with his family about his time in the Rising, or his detainment at His Majesty's pleasure.
"But my grandmother did tell of one time when she urged him to follow up on a missed payment of his military service pension and his response, though brief, was filled with emotion: 'I didn't go out to fight for a bloody pension!' he said and left the room.
"After my father's funeral in February last year, my cousin Helen Kelly and I agreed it was important to get the story of our grandfather together for the family, before it missed another generation and was potentially lost forever.
"Through his pension application and stories from aunts and uncles, we pieced together his life story, including his role in the Rising, and called the 120-strong extended family together in the local community hall, to share it with them.
"He died in 1945 and had 23 grandchildren, none of whom got the chance to meet him."
Declan and Helen went to visit the place where their grandfather had fought - and got quite a surprise when they got there.
"There's nothing to mark what happened during the Rising. I contacted the Mendicity Institution, and the HSE, which leases the building on Usher's Island, to see how they'd feel about us putting up a plaque. They said it was no problem.
"We networked through the 1916 Relatives' Association and formed the Mendicity Garrison Relatives Group last November. So far we've traced nearly all of the families of the garrison combatants, but we haven't yet been able to track down anyone related to Seán Heuston - so if one of his kin is reading this, please get in touch.
"We'll have an official unveiling of the plaque some time between early March and April 24 next year. The wording will be in English and Irish and it will include the names of each of the combatants. I think that's a fitting tribute to a group of men who fought so valiantly for Irish freedom."