The Prince of Wales and the Duchess of Cornwall are in County Wicklow as part of a two-day visit to the Republic of Ireland.
The royal couple will afterwards travel to Northern Ireland.
They were met at Glencree Centre for Peace and Reconciliation by President Michael D Higgins and his wife Sabina.
Former taoiseach Bertie Ahern and former Northern Ireland first minister Peter Robinson were among those at the event.
It included musical performances and poetry reading.
This is Prince Charles' fifth visit to the Republic of Ireland in the past five years - nearly always on dates in May.
All of them have emphasised the themes of peace and reconciliation.
Speaking in the grounds of Powerscourt House at an event hosted by Wicklow County Council, the Prince of Wales said what was most special about coming to Ireland was being able to "celebrate and remind ourselves of those vital links between us that go back hundreds, if not thousands of years".
He said: "Whatever happens, the great thing is to go on to understand how much we mean to one another."
He thanked the public for what he described as "putting up with us yet again" as he said he and his wife "attempt to cover all the counties before we completely disintegrate".
In the shadow of the Sugarloaf Mountain, Prince Charles and Camilla were shown the Italian Gardens and met with the Slazenger family who run the estate, before Prince Charles planted a Giant Redwood tree in the gardens.
The Sequoiadendron giganteum is the largest tree species in the world and should live for 1,000 years.
Prince Charles also said he discovered that, like most tree-planting he takes part in, the tree he planted at Powerscourt will be dug up and replanted at a better time of year. But he said he hoped to return to see how it is growing in the future.
The Duke of Wellington gifted 100 of these trees to Lord Powerscourt for helping him secure the victory at the battle of Waterloo.
The Prince of Wales will now visit the Cool Planet Experience, an attraction which focuses on the themes of climate change.