Motorists and commuters were bracing themselves for traffic chaos as the Republic's largest ever security operation swung in to action for Queen Elizabeth's visit.
Road closures and parking restrictions are already in place in parts of Dublin as the capital prepares for a lockdown during the historic four-day royal visit.
Armed British police officers will patrol the streets alongside gardai and soldiers to protect the 85-year-old monarch and the Duke of Edinburgh, Prince Philip, as they travel to engagements.
Taoiseach Enda Kenny said Government and police were conscious of security threats, but maintained the Queen would receive a warm welcome from the vast majority of Irish people.
He described her visit as the start of a new era between the two counties based on respect, friendship and mutual recognition. "The visit of the Queen is symbolically a healing of the past and facing with courage to the future," Mr Kenny told told Sky news.
The royal visit is the first by a British sovereign to the Republic. Her grandfather King George V visited the country when it was under British rule 100 years ago.
Protesters - led by socialist republican group Eirigi - are already attempting to set up an Irish Freedom Camp on Parnell Square close to the Garden of Remembrance, which honours all those who fought for Irish freedom. The Queen is due to attend a wreath-laying ceremony there on Tuesday afternoon.
Her arrival on Tuesday morning has also sparked controversy as it coincides with the 37th anniversary of the Dublin and Monaghan bombings, which killed 34 people. Victim groups believe the bomb attacks were carried out by loyalist paramilitaries with British state collusion.
Security chiefs said activists will not get near the Queen, with up to 4,000 garda officers on the streets at any one time in Dublin alone.
Surveillance has been stepped up on known republican dissidents, with several arrests made in the north and south of Ireland. Among them was veteran republican Marian Price who has been charged by police investigating a dissident republican rally in Londonderry on Easter Monday. The 57-year-old will appear in court in the city on Monday accused of encouraging support for a proscribed organisation.