In the '60's I visited Dublin Castle with my Uncle, Walter Robert Fitz-Henry, and saw a foundation stone, I think in the south west tower, which had an inscription naming Meiler FitzHenry as the person who had laid that stone and it also stated that he was the first Justiciar of Ireland. The date on the stone was about 1167. The tower has since disappeared.
On subsequent visits some years following that first visit there remained no trace of the Foundation Stone. On enquiring information from the curator of Dublin Castle museum, on one of those visits, he said that he had no knowledge of such a stone, but guessed that during restoration of the castle that, if it was there, it had probably been dumped together with lots of rubble in Dublin bay north east of the Bull wall.
Typical , you would think they conserve that history , sad
Did you read this book about Meiler Fitzhenry ?