Relatives of those killed and injured on Bloody Sunday took part in a remembrance walk to mark the 50th anniversary of the atrocity on Sunday morning.
The event is one of a series taking place over the weekend in Derry.
13 civil rights protesters were shot dead by British soldiers on January 30, 1972 in the city.
Another man shot by paratroopers on the day died four months later.
While many consider him the 14th victim of Bloody Sunday, his death was formally attributed to an inoperable brain tumour.
On Sunday, the crowd gathered at Creggan Shops before making their way to the Bloody Sunday Monument in Rossville Street for the annual memorial service and wreath-laying ceremony at 11am.
Taoiseach Micheal Martin laid a wreath on behalf of the government and said it was a "privilege" to be with the families of victims of Bloody Sunday.
He also thanked them for their "dignified, persistent and courageous" campaign to pursue justice, truth and accountability.
Mr Martin said: "Today we remember all those who died or were injured as a result of the atrocity on Bloody Sunday, one of the darkest days for this island.
"We also pay tribute to the families of the victims, whose dignity and persistence in the search for truth and justice has never wavered."
Later, President Michael D Higgins will deliver a recorded message to the Bloody Sunday families.
The president's message will be shown publicly during the commemorative event Beyond the Silence, which will take place before a limited audience in Millennium Forum Theatre.
His message will be broadcast on a large screen and the occasion will be livestreamed to an online audience.
The event will be hosted by actor Adrian Dunbar and will feature tributes to the victims, as well as music and public performances.
The forum will fall silent on Sunday at the precise time when 50 years earlier paratroopers opened fire on civil rights marchers in the Bogside.
Tanaiste Leo Varadkar said: "Today we remember the 14 innocent people who were killed in Derry 50 years ago on Bloody Sunday.
"The events of that day cast a long shadow over the city and the country that many are still dealing with today.
"We salute the courage and perseverance of the victims and their families who have campaigned tirelessly for justice and who continue to do so today.
"Their tenacity serves as an example to other Troubles-related victims to never give up the fight for justice.
"We pledge to honour the memory of those who died on Bloody Sunday by standing with all victims of the Troubles and continuing to work for permanent peace on our shared island."
