Queen Elizabeth II's signature in the visitors book at Aras An Uachtarain in Dublin,Ireland. An unprecedented security operation is taking place with much of the centre of Dublin turned into a car free zone. (Irish Government /Pool/Getty Images) #

Britain's Queen Elizabeth II looks back at Irish Defence Guard Chief of Staff, Lt. Gen. Sean McCann, at the Aras an Uachtarain, the president's official residence, in Dublin on the first day of her four-day visit to Ireland, May 17, 2011. (Peter Muhly/AFP/Getty Images) #

Irish riot police officers stand amongst bricks thrown by protesters in the streets adjacent to the Garden on Remembrance where Queen Elizabeth II laid a wreath, May 17, 2011 in Dublin, Ireland. (Oli Scarff/Getty Images) #

A demonstrator is arrested by Irish riot garda during a protest in Dublin on the first day of Queen Elizabeth II's four-day visit to Ireland. At least 100 protesters chanted slogans and torched the British flag in Dublin, May 17, 2011. (Carl de Souza/AFP/Getty Images) #

A demonstrator throws a brick at Irish Riot Garda during a protest in Dublin on the first day of the Queen Elizabeth II four day visit, May 17, 2011. (Carl de Souza/AFP/Getty Images) #

A protestor tries to pull a barrier from a police line during a demonstration in Dublin against the visit of Britain's Queen Elizabeth II, on the first day of her four-day visit to Ireland, May 17, 2011. There were two republican rallies near the Garden of Remembrance -- a memorial to those who died fighting for Irish independence -- where the Queen visited later in the day in one of the most sensitive moments of the trip. (Carl de Souza/AFP/Getty Images) #

Queen Elizabeth II, President Mary McAleese, Prince Philip, The Duke of Edinburgh and Dr. Martin McAleese walk down to tree planting ceremony in Aras An Uachtarain, May 17, 2011. (Irish Government/Pool/Getty Images) #

Britain's Queen Elizabeth II plants a tree during a ceremony as Irish President Mary McAleese watches, at the Aras an Uachtarain, the president's official residence, in Dublin, May 17, 2011. (Maxwells/AFP/Getty Images) #

Britain's Queen Elizabeth II meets students and staff at Trinity College Dublin. The Queen set foot on Irish soil at the start of a historic state visit which will herald a new era in relations between Britain and the Republic. Politicians on both side of the Irish Sea have described the four-day event as momentous. (Tony Maxwell/Irish Government Pool/Associated Press) #

Irish Garda form a police line during a protest in Dublin against the visit of Britain's Queen Elizabeth II, May 17, 2011. (Carl de Souza/AFP/Getty Images) #

A woman is detained by riot police during disturbances in north Dublin, May 17, 2011. (Cathal McNaughton/Reuters) #

Protestors gather in Dublin to demonstrate against the visit of Britain's Queen Elizabeth II to Ireland on the first day of her four-day visit, on May 17, 2011. (Carl de Souza/AFP/Getty Images) #

Queen Elizabeth II accompanied President Mary McAleese for a wreath laying ceremony at the Garden of Remembrance on May 17, 2011. (Irish Government/Pool/Getty Images) #

Queen Elizabeth II and Prince Philip, Duke of Edinburgh, are shown the Book of Kells during a visit to Trinity College Dublin, May 17, 2011 in Dublin, Ireland. (John Stillwell/Pool/Getty Images) #

Britain's Queen Eliazbeth II accompanied by Ireland's President Mary McAleese arrive to lay wreaths in the Garden of Remembrance in Dublin, Ireland, May 17, 2011. (Paul Ellis/AFP/Getty Images) #

Irish police officers stand against demonstrators in north Dublin, May 17, 2011. Britain's Queen Elizabeth arrived in Dublin on Tuesday for a historic state visit steeped in symbolism and surrounded by security after a makeshift bomb was found, highlighting the lingering hostility of a small minority. (Darren Staples/Reuters) #

A woman wearing a face mask depicting Britain's Queen Elizabeth II waits for the Queen's motorcade to pass on a balcony in central Dublin, May 18, 2011. Queen Elizabeth is on the second day of her first-ever state visit to Ireland. (Tim Hales/Associated Press) #

Armed Irish police officers guard the Irish War Memorial Gardens at Islandbridge during a visit by Britain's Queen Elizabeth and Ireland's President Mary McAleese in Dublin, May 18, 2011.(Dylan Martinez/Reuters) #

Queen Elizabeth II lays a wreath of poppy flowers at the Irish War Memorial Garden in Islandbridge, May 18, 2011 in Dublin, Ireland. (Oli Scarff/Getty Images) #

Britain's Queen Elizabeth II passes a crowd of well-wishers during her visit to the Irish War Memorial Gardens at Islandbridge in Dublin, May 18, 2011. (Dylan Martinez/Reuters) #

A member of the Irish military relaxes after Queen Elizabeth II and the Irish President Mary McAleese laid wreaths at the Irish War Memorial Garden, May 18, 2011. (Oli Scarff/Getty Images) #

A lady vacuums the red carpet in advance of a visit by Queen Elizabeth II and Prince Philip, Duke of Edinburgh to some government buildings, May 18, 2011. (Irish Government/Pool/Getty Images) #

Britain's Queen Elizabeth II meets Irish Prime Minister Enda Kenny, at the Government Buildings in Dublin, on the second day of the Queen's four-day visit to Ireland, May 18, 2011. (Mark Cuthbert/AFP/Getty Images) #

Britain's Queen Elizabeth II and Prince Philip,The Duke of Edinburgh, visit the Guinness Storehouse Gravity Bar in Dublin, May 18, 2011.Queen Elizabeth and her husband Prince Philip resisted the temptation to sup the perfect pint of Guinness on a visit to the Irish cultural icon's home brewery. (Maxwells/AFP/Getty Images) #

Britain's Queen Elizabeth II is flanked by President Mary Mc Aleese and Christy Cooney, President of the Gaelic Athletics Association (GAA), as they walk onto the pitch at Croke Park in Dublin, May 18, 2011. Queen Elizabeth II visited the scene of a massacre by British forces during Ireland's independence struggle on the second day of her groundbreaking state visit to the republic. (Irish Government/AFP/Getty Images) #

Irish police watch from a floodlight gantry, as Britain's Queen Elizabeth II visits Croke Park Stadium, in Dublin, May 18, 2011, site of a notorious massacre where British troops killed 14 Irish civilians in 1920. The Queen's visit to Croke Park on the second day of her historic trip to the Republic of Ireland highlights the vast improvement in Anglo-Irish relations since those dark days. It brought the English monarch to a large sports stadium that is a revered spot for Irish nationalists who mourn those who died there during the conflict with Britain.(Peter Morrison/Associated Press) #

A protestor is restrained outside Dublin Castle ahead of the state dinner in honor of Britain's Queen Elizabeth II on the second day of her four-day State Visit to Ireland, May 18, 2011. (Niall Carson/Associated Press) #

Queen Elizabeth II arrives to attend a State Banquet in Dublin Castle with Irish President Mary McAleese, May 18, 2011 in Dublin, Ireland. (Oli Scarff/Getty Images) #

Britain's Queen Elizabeth II makes her speech in Dublin Castle during the state dinner on the second day of her four-day state visit to Ireland, May 18, 2011. Queen Elizabeth II made a powerful statement expressing "deep sympathy" to all who had suffered as a result of the troubled relations between England and Ireland. She did not apologize for any British actions during the bitter conflicts between the two neighbors but said it is clear mistakes were made. "To all those who have suffered as a consequence of our troubled past I extend my sincere thoughts and deep sympathy," she said. "With the benefit of historical hindsight we can all see things which we would wish had been done differently or not at all." (Pool/Associated Press) #

Garda on horseback form a protective ring around Dublin Castle as the Queen attends a state dinner, May 18, 2011. (Chris Jackson/Getty Images) #

Queen Elizabeth II and Chryss O'Reilly, Chair of the Board of The Irish National Stud, tour the Irish National Stud, during the third day of the state visit to Ireland, May 19, 2011 in Kildare, Ireland. (Irish Government/Pool/Getty Images) #

Queen Elizabeth II receives flowers from Emma Osbourne with John Osbourne, CEO of The Irish National Stud (R) and Chryss O'Reilly , Chair of the Board of The Irish National Stud, May 19, 2011. (Irish Government/Pool/Getty Images) #

Queen Elizabeth II and John Osbourne view Stallion handler Paul Croke with "Jeremy", in the Stallion Yard of the Irish National Stud, May 19, 2011 in Kildare, Ireland. (Irish Government/Pool/Getty Images) #

Britain's Queen Elizabeth II on the third day of a four day state visit to Ireland which is the first state visit by a British monarch since Ireland's independence. (Cathal McNaughton/Reuters) #

Britain's Queen Elizabeth II with sculptor Anthony Scott after unveiling a sculpture during a tour of the Irish National Stud in Kildare, May 19, 2011. (Maxwells/AFP/Getty Images) #

Fishmonger Pat O'Connell shows his wares to Britain's Queen Elizabeth II during a visit to the English Market in Cork, May 20, 2011, on the fourth and final day of her first-ever state visit to Ireland. The ambitious trip has been hailed by many as consolidating a new era of cooperation between England and Ireland, (Pool/AP) #