Sometimes words aren't necessary. That was the case Tuesday when Queen Elizabeth II placed a wreath in Dublin's Garden of Remembrance to honor the Irish rebels who lost their lives fighting for freedom — from Britain.

The queen became the first British monarch to set foot in Dublin for a century. Her four-day visit is designed to show that the bitter enmity of Ireland's war of independence 90 years ago has been replaced by Anglo-Irish friendship, and that peace has become irreversible in the neighboring British territory of Northern Ireland.

The ceremony under threatening steel-gray skies was simple and direct, its meaning clear. There were no apologies, no acknowledgment of misdeeds, but the presence of the British monarch on ground that is sacred to many Irish was a powerful statement of a desire to start anew.

Helicopters and fixed-wing aircraft patrolled the skies and marksmen kept watch on rooftops during the ceremony for any attempt by Ireland's most extreme nationalists to disrupt the event.

A few hundred supporters of Irish Republican Army dissident groups did clash with police on the security perimeter a half-mile (1 kilometer) away, but the trouble didn't interrupt the queen's carefully choreographed procession through Dublin.

Nor did the dissidents' efforts overnight to draw attention to themselves by planting a pipe bomb in a bus 15 miles (25 kilometers) away from Dublin and three hoax devices in the city itself.

Later, the dissident IRA protest degenerated into hooliganism along a working-class street of inner-city Dublin where anti-police sentiment typically runs high.

Scores of teenage boys and young men, some masked, threw lit firecrackers, flares and beer bottles at a line of helmeted, shielded riot police among dilapidated small shops and fast-food joints on Dorset Street. They set fire to the contents of garbage cans on side streets.

Police "snatch squads" surged forward occasionally to arrest individual rioters. By nightfall, at least 21 people were in custody. Police said no officers or civilians suffered any serious injuries.

Earlier, as the queen stood in silence alongside Irish President Mary McAleese, a flock of black balloons floated off in the distance, a silent protest by the nationalist Sinn Fein party.

But the event marked a successful first day of the queen's groundbreaking four-day visit to Ireland, a trip aimed at demonstrating that the former foes have reconciled their differences amid strong ties of culture and immigration, common economic interests, and a joint desire to bury the painful past.

Mary Daly, a historian and director of the College of Arts and Celtic Studies at University College Dublin, said the queen's gesture will be widely understood in Ireland.

"It's not uncommon for a head of state to lay a wreath at a site of mourning, but in this case you get the British monarch laying a wreath at a memorial garden that remembers many people who took up arms against her ancestors," she said. "What it reflects is sympathy, recognition of this independent Irish nation, the legitimacy of its cause, and it's a mark of mutual respect. That's why it's very, very important."

The painstakingly choreographed visit has been designed to highlight today's exceptionally strong Anglo-Irish relations and the slow blooming of peace in neighboring Northern Ireland following a three-decade conflict that left 3,700 dead.

The queen arrived 100 years after her grandfather George V visited Dublin when Ireland was still part of the British Empire. Her visit prompted the most extensive security operation in the history of the Irish republic, with some 8,500 police on the streets to thwart attacks. All leaves were canceled, troops were on standby, and much of central Dublin was off-limits to motorists and pedestrians.

Police scuffled with small groups of anti-British protesters at two spots on the edge of the security perimeter. Many waved placards that read "Britain out of Ireland," referring to the fact that Northern Ireland remains part of the United Kingdom.

At one flashpoint involving about 50 protesters, officers used pepper spray to prevent a few men from breaching security barriers, then police on horseback drove back the crowd.

At the other trouble spot, protesters tried to block Dublin's major thoroughfare, O'Connell Street, but were pushed to the sidewalk by police. No serious injuries were reported.

The protesters were outnumbered by several thousand well-wishers hoping to get a glimpse of the queen and her husband, Prince Philip. Crowds clapped and cheered when she left Trinity College after viewing rare books, including the Book of Kells, a celebrated 9th-century gospel manuscript.

Police made it extremely difficult for protesters to get within sight of any of the queen's engagements. Onlookers were given few vantage points to see the queen unless they had been included in carefully vetted guest lists.

The queen tailored her arrival outfit to her destination, stepping off the plane resplendent in a cloak of emerald green and a dress of St. Patrick's blue. She later changed into an ivory outfit trimmed with green. Both outfits were topped with the fanciful hats that are her trademark.

She had been invited to Ireland by President McAleese, a Belfast-born Catholic who has spent 14 years lobbying the queen to make the journey in the name of peace.

McAleese welcomed the queen by saying that Britain and Ireland were "determined to make the future a much, much better place."

The queen didn't comment ahead of her planned speech Wednesday night at Dublin Castle, the former seat of British rule of Ireland.

A 33-motorcycle police escort led the queen to McAleese's residence in Dublin's vast Phoenix Park through the unusually empty streets of Dublin — cleared to ensure no anti-British extremist could get close enough to launch an attack.

Nearby Dublin Zoo was closed as a security precaution and no civilian aircraft were permitted over central Dublin for the day.

The queen's visit to the Garden of Remembrance also showed that at 85 she still has the stamina for challenging events, walking a lengthy stretch beside a reflecting pool before climbing 28 stone steps without faltering to reach a sculpture honoring the dead.

Sinn Fein lawmaker Aengus O Snodaigh, who helped release the black balloons, said they were intended to symbolize the hundreds killed by British troops in Northern Ireland and the 33 people killed in no-warning car bomb attacks in Dublin and the border town of Monaghan in May 1974.

"We are living in changed and changing times," O Snodaigh said. "But the fact that Dublin city is on lockdown for the week makes it clear that the relationship between the two islands is still not 'normal.'"

Nonetheless, Sinn Fein itself has embraced peace after supporting the IRA's efforts to overthrow Northern Ireland by force. That fruitless campaign formally ended with the IRA's disarmament in 2005. It paved the way for a surprisingly stable coalition government today in Belfast involving Sinn Fein and their former enemies in the British Protestant majority there.

The northern peace leaves only small bands of IRA dissidents to carry on a largely symbolic campaign. They mounted a few token efforts of opposition Tuesday that grabbed headlines but failed to disrupt anything.

Irish Army experts overnight defused one pipe bomb on a Dublin-bound bus that was detected in Maynooth, 15 miles (25 kilometers) west of the capital. Police said the bomb was properly constructed but not primed to detonate.

A second device abandoned near a light-rail station in west Dublin was deemed a hoax Tuesday morning. Later, police responded to at least two more reports of suspicious packages in working-class districts of north Dublin, but no further bombs were confirmed.

Police said IRA dissidents using a recognized codeword warned about the bus bomb, which was left in overhead luggage.

Irish and British officials were keen to stress that the queen's visit to Dublin, Kildare, Tipperary and Cork would proceed as planned — accompanied by the biggest security operation in the Republic of Ireland's history.

"This is the start of an entirely new beginning for Ireland and Britain," said new Irish Prime Minister Enda Kenny. "I really do hope that the welcome she gets will be genuine and memorable for her."