A lost batch of letters to and from Roger Casement was last night described as a very significant find by Fianna Fáil senator Martin Mansergh.
The public will be able to view the letters for the first time from today.
At a reception to launch the collection last night in Ennis, Senator Mansergh said the letters are of considerable importance and add another dimension to the study of Roger Casement.
The 50 letters had been stored away under lock and key and possibly forgotten about for over 30 years before Clare County Council archivist Róisín Berry discovered them during a trawl of the vast council archive in 2003.
In an accompanying statement released with the archives last night, a leading expert on Casement, Angus Mitchell, said that the discovery of the letters "is a small jewel" to historians involved in Casement studies.
Mr Mitchell said that scrutiny of letters between Casement and an old German friend from his days in Africa, Count Gerhard Blücher, "enables a number of old biographical myths to be more critically examined and laid to rest".
The letters concern the last three years of Casement's life, from his arrival in Germany in 1914 to the very month he leaves Germany in 1916 on the U-19 submarine bound for Ireland.
The documents address a range of subjects including the enlisting of Irishmen in the first World War, the appointment of an envoy from England to the Vatican, the Findlay affair, the work of Father Crotty in German prison camps, writing articles for the press, keeping a diary, and the desire for peace.
Mr Mitchell said evidence from the letters should persuade a new generation of historians that a combination of isolation, disillusionment and depression, largely resulting from Casement's hatred of the first World War, was at the heart of his breakdown.
"What comes across most strongly, however, is Casement's inextinguishable passion and drive for the cause of Irish independence, reflected also in his writings from the period."
The last letter on file is one from Casement, dated April 4th, 1916, just 11 days before his departure for Ireland on a German U-boat, which landed him at Banna Strand, Co Kerry, on Good Friday, 1916.
The letters had been in the council's archive since the late 1960s after being donated by the late Ignatius M. Houlihan, who had received a gift of the papers from a member of one of the noble families in Europe.
Ms Berry said yesterday she came across the papers during an inventory of the archives. "At first, I did a double take, I wasn't expecting something so exciting. I instantly recognised the value of them and I was anxious to make them accessible as soon as possible."
Mr Mitchell said although there is plenty to suggest that significant parts of the Casement archive have, over the years, been lost or destroyed, the discovery of the Casement-Blücher letters confirms that history is not a fixed science capable of definite truths.
Born in Dublin in 1864, Casement had a successful career with the British Foreign Office before resigning from the service in 1913 due to ill-health. He returned home to Ireland when he put his energies towards achieving an independent Ireland.
The "Casement in Germany" exhibition will run from today to Friday June 3rd in Clare Museum's Westropp Room.