Many of these items were previously not known to have existed. For the Co Mayo man, the collection was completed in 1993 when he purchased an original copy of the 1916 proclamation. He told his wife Anne that he had acquired "the holy grail".

Today, there are fewer than 20 surviving copies of the original proclamation which was read by Padraig Pearse on Easter Monday morning from the steps of the GPO in Dublin. A value of 140,000 to 180,000 has been placed on another original copy due to be auctioned this week in Dublin.

Probably even more significant, however, is the little-known proclamation of 1917 which is also in the Jackie Clarke Library. As the first anniversary of the 1916 Rising approached, a reprint of Pearse's proclamation was organised by a group of republican women on the same press as the original document. It was distributed in Dublin to commemorate the events of the previous year and is believed to be rarer . . . and more valuable . . . than the original proclamation.

Padraig Pearse was executed by the British on 3 May 1916 for his role in the rebellion. The Jackie Clarke collection contains a letter written by the governor of Kilmainham Gaol, dated 2 May 1916, requesting the Catholic priest Fr Aloysius to come to the prison to give Pearse the last rites. "The prisoner HT Pearse desires to see you and you have permission to visit him, " the governor writes . . . in error as the Rising leader was known as PH Pearse. A written note from Fr Aloysius is also included.

"This is the summons to attend the late PH Pearse.

I received it at about 10pm on 2 May. Upon arrival at Kilmainham I was notified that Thomas McDonagh also desired my services. The executions took place at about 3.30am on 3 May."

There are many other unique items relating to the 1916 Rising in the Jackie Clarke Library. These include three letters used by the British military as evidence in Eamon Ceannt's court martial. These letters, one of which was sent by Ceannt . . . a signatory of the proclamation . . . to Cathal Brugha, were previously not known to exist. Ceannt was executed on 8 May 1916, four days after another leader of the rebellion, Joseph Mary Plunkett. Books from Plunkett's own library are in the Ballina collection, including what appears to be a previously unpublished poem, 'The Sceptic', in Plunkett's own handwriting, and a rare copy of Sonnets to Columba, a limited edition of less than 25 privately-printed love poems for one of his early girlfriends.

Literary scholars will be interested in several items relating to Thomas McDonagh, including a small black-covered notebook from his time in Paris which contains handwritten comments in French. McDonagh destroyed many of his poetry books as he was unhappy with the quality. One of the books obtained by Jackie Clarke has handwritten amendments and textual changes to several poems. Historians have clashed about whether McDonagh actually made a speech at the court martial which confirmed he would be executed for his role in the rebellion. However, the Clarke collection contains a typed British military transcript of McDonagh's speech at his court martial which appears to be the closest yet to the words actually spoken by the Co Tipperary republican.

Among the other 1916-related documents are copies of War News, the republican publication issued during the Rising and 50 different newspapers from Easter week. Few republican leaders from the period are missing in the material collected by Jackie Clarke. Among the items he acquired was a small prayerbook given by Tom Clarke to his sister as a Christmas present after his release from Portland Prison in 1898.

The boxes in the collection are filled with thousands of handbills and leaflets covering all eras of republican history, including a 1910 notice from New York featuring a very rare picture of a young James Connolly. Described as the "national organiser of the Socialist Party of Ireland", his American supporters were organising a farewell dinner for Connolly at Cavanagh's Restaurant on Eighth Avenue.

"Don't miss this occasion to tell Connolly what you think of him, " the notice declares. Admission to the dinner was $1, a considerable sum of money in 1910. Those attending were promised a "night of Irish rebel song and story".

The collection also includes documents relating to Roger Casement's time in the British civil service, including a letter written in 1897 when he was British consul to the governor of Mauritius. The letter was purchased by Jackie Clarke in 1990 . . . a price of £120 to £160 is written in pencil on the back of the document. The Ballina man also acquired maps and other memorabilia including the Boer War flag flown by John McBride's Irish brigade in 1899.

One of the gems in a collection of many treasures is an autograph book which includes the signatures of all the members of the first Dail. The opening signature is that of Eamon de Valera, dated just days after the terms of the Anglo-Irish Treaty were agreed in London in December 1921. The treaty was then debated by the Dail and the owner of the autograph book collected the signatures of the republican politicians involved. On 7 January 1922, the day the Dail ratified the Anglo-Irish Treaty, Michael Collins wrote in the autograph book: "Let the Irish nation judge us now and for future years".

Seven months later, Collins was shot dead as the country split over the treaty terms. The unique autograph book may have been compiled by Mary McSweeney, who opposed the treaty. Alongside Collins' entry, McSweeney wrote, "The last moment of the betrayal of the Irish people".

The oldest manuscript in the collection dates from 1617 and is a copy of a land ownership transfer in the 'City of Corke', although a map of Mayo is believed to date from the 16th century.

Other items from the 17th century include a copy of the London Gazette newsletter from 1690, published just before the siege of Limerick, which chronicles the process of the military campaign in Ireland. Another letter on parchment is in the hand of the earl of Tyrconnell, secretary to James II, and dated November 1688.

Only five handwritten letters from Wolfe Tone are known to exist and two of them are in the Jackie Clarke Library in Ballina. One of these items is dated 1 May 1798. Historian Sinead McCoole made a fascinating discovery when she came across a modern envelope on which Jackie Clarke had scribbled a note. "This envelope contains Wolfe Tone's cockade worn at his trial, " Clarke wrote. Somehow, during his life of collecting historical material, Jackie Clarke had acquired the famous cockade from the hat Wolfe Tone wore when he was convicted of treason in 1798.