Actor Adrian Dunbar lent his star power to the campaign to preserve the Moore Street site as the last battlefield of the 1916 Rising.
Mr Dunbar is supporting the long-running campaign that is trying to stop UK property company Hammerson from developing a 5.5-acre site which includes many locations where the 1916 Rising rebels surrendered after leaving the GPO.
The project known as Dublin Central would, the developers said, revitalise the north inner-city area.
Mr Dunbar said he was “delighted” to help the cause and to meet so many of the relatives of those who had been in the GPO in 1916.
A crowd of several hundred gathered outside the GPO to meet the actor. Among them were the former president of Sinn Féin Gerry Adams and the current leader of the party Mary Lou McDonald.
Later, Mr Dunbar paused in O’Rahilly Parade to read the last letter from The O’Rahilly, who bled to death in the alleyway off Moore Street on the last day of the 1916 Rising.
The tour of Moore Street and its environs was led by Honor Ó Brolcháin, a grandniece of Joseph Plunkett (one of the signatories of the Proclamation), and by Patrick Cooney, the founder of the Saving Moore Street campaign.
The tour took in Henry Place, a dog-leg street that used to back on to the side door of the GPO.
Mr Cooney said the more they have investigated the site, the more they have realised that many buildings that were thought to be modern constructs actually only had modern facades.
He said the preservation of 10-25 Moore Street, the last gathering place of the 1916 Rising rebels, is still standing and this was down to the campaign. “At the end of the day, the developer will have a postage stamp to develop on and we will walk away or we will push him away,” he said.
“We might need to occupy the buildings again and we might need numbers. I know Gerry Adams has offered to be the first man in.”
He said they had won the last time in court but that the development would soon come to court again.
Last month Hammerson submitted further planning applications for the site which would see the transformation of an area bound by O’Connell Street, Parnell Street and Moore Street.