Queen Elizabeth II starts her historic state visit to Ireland Tuesday amid a massive security lockdown after the threat of Irish republican terrorism resurfaced with a coded bomb threat in London.
The historic four-day trip, the first by a British monarch to the Republic of Ireland since it gained independence from London in 1922, is a landmark moment aimed at normalising relations between the two neighbouring states.
However, a visit intended to underline the progress made following the hard-won peace in Northern Ireland is taking place surrounded by the highest security.
Central Dublin was in a police clampdown amid Ireland's biggest-ever security operation, while dissident republicans opposed to the peace process and the sovereign's visit made a coded bomb threat in London on Monday.
Police sealed off roads near Buckingham Palace and carried out a controlled explosion after the first coded warning outside Northern Ireland for 10 years.
Such warnings have traditionally been used by Irish republican paramilitaries before attacks.
Dissidents opposed to the peace process have been resurgent in Northern Ireland in recent months, murdering a Catholic policeman in a car bombing in April.
Opposition to the queen's visit persists among hardcore and violent republicans, who want Northern Ireland to become part of the Republic.
However, they are a small minority and officials are doing their best to ensure the 85-year-old queen and Prince Philip receive a warm welcome.
"We've had a long relationship; sometimes it's been very close, sometimes it has been acrimonious, but over the past number of years, we have had a very warm friendship," he told AFP.
"They are our closest trading partner, they are our neighbours who helped us out during the recent IMF (International Monetary Fund) bailout, and we rely so much, for trade and for tourism, on the United Kingdom."
A 10,000-strong force is being deployed at an estimated cost of 30 million euros ($42 million), with reports saying even the navy will be deployed off the Dublin coast to prevent against a possible missile strike from the sea.
The royals will fly into Casement Aerodrome, southwest of the capital.
The former Baldonnel military airbase was renamed in 1965 after Roger Casement, an Irish nationalist executed for treason by the British in 1916.
The authorities spent Monday combing the sides of the road outside the airbase with police stationed along the perimeter.
The queen's arrival coincides with the 37th anniversary of the Dublin and Monaghan bombings, perpetrated by the Ulster Volunteer Force, a loyalist Protestant paramilitary group. Some 34 people were killed, making May 17, 1974 the deadliest day of the three decades of strife known as the Troubles.
In an open letter to the queen, survivors and victims' families have pressed for Prime Minister David Cameron to release files about the incident they claim were withheld from an Irish judge who investigated the bombings, amid allegations of British collusion.
The Aras dates back to 1751 and used to house the viceroys who oversaw British rule in Ireland. Queen Victoria and King George V stayed there while visiting.
George V, Queen Elizabeth's grandfather, was the last British monarch to visit, 100 years ago.
Following talks, the queen and the president head straight for one of the most sensitive moments of the trip -- a visit to the Garden of Remembrance, dedicated to "all those who gave their lives in the cause of Irish freedom".
Both McAleese and Queen Elizabeth will lay wreaths and the national anthems of both states will be played.
Republican demonstrators will be kept far from the scene, with many of the surrounding roads completely screened off.
The couple's final engagement Tuesday will be to visit Trinity College, one of Europe's finest universities, where they will view the Book of Kells, a ninth century gospel manuscript.
Source: AFP European Edition