Britain's Queen Elizabeth II has arrived in the Irish Republic - the first ever visit there by a British monarch.
Queen Elizabeth and her husband Prince Phillip received a state welcome upon the start of their four-day visit Tuesday, just hours after a series of bomb threats in both countries.
Some 8,000 police were deployed to protect the British monarch, clearing the streets of Dublin to prevent any potential attack.
Members of a violent IRA splinter group opposed to Britain's continued rule in Northern Ireland are believed to be behind the threats.
Dressed in green, the symbolic color of Irish Catholics, the queen met Tuesday with Irish President Mary McAleese. She then went on to visit a memorial honoring Irish war dead.
McAleese described the historic visit as an extraordinary moment in Irish history and a sign of the success of the peace process that ended decades of violence in Northern Ireland.
King George V was the last reigning British monarch to visit what is now the Irish Republic. He did so in 1911, when it was still part of the United Kingdom.
The queen and Prince Philip are traveling in an armored Range Rover, on loan from the British province of Northern Ireland to the independent south of the island.
British Prime Minister David Cameron is due to join the queen on Wednesday.
The Irish military on Monday defused a bomb found in the luggage compartment of a bus near Dublin.
Shortly after, a second suspicious device was found at a nearby tram station and determined to be a hoax.
London authorities received a coded bomb threat warning on Monday, leading police to block off streets near Buckingham palace and sweep the area.
Some information for this report was provided by AP and Reuters.