Resplendent in a crystal-embroidered ivory ensemble that cut through the gloom of a relentless drizzle, Queen Elizabeth II and a nation marked her 60th year on the throne Sunday with a dazzling flotilla of 1,000 ships down the Thames in a display of pageantry the likes of which have not been seen here in about 350 years.

The flotilla — the highlight of a four-day Diamond Jubilee celebration commemorating a woman who has reigned longer than any British monarch save Queen Victoria — brought more than 1.2 million onlookers who jostled for position along a seven-mile stretch of the river. Standing under a gilded canopy on the top tier of a royal barge, the queen, 86, her most important family members at her side, offered her famous flutter of a wave as trumpeters, tolling bells and a floating London Philharmonic Orchestra provided a majestic soundtrack.

The grandeur on the river underscored a burst of affection for the queen brought about by the jubilee. The milestone comes as the House of Windsor is enjoying surging popularity at home and abroad following last year’s royal wedding of the queen’s grandson, Prince William, to his bride, Catherine, a graceful young woman who has emerged as a fashion icon and global celebrity. But in a bow to the draw of the monarch, the crowds here topped even those of the royal nuptials, held on an idyllic spring day last year totally unlike the dark, wet and cold afternoon in London on Sunday.

For Britons, who often delight in describing their American cousins as gushing patriots, the event saw them in the midst of their own full-throttle celebration of nationhood that seemed like the Fourth of July on steroids. A sea of waving Union Jacks lined the Thames, with the red, white and blue British flag festooned over thousands of street parties across the nation. Stirring verses of “Rule, Britannia!” came from loudspeakers on boats on the river. As the queen’s barge passed by, even young children watching with their families spontaneously began singing, “God Save the Queen.”

“Oh, there’s no doubt about it, today is a day when we are all proud to be British,” said Erika Keat, 29, who was wearing a bowler hat in the colors of the union jack as she watched the pageant with tens of thousands of onlookers gathered at London’s riverside Battersea Park. “And with all due respect to the Americans, no one does pomp and ceremony like us.”

The day, however, was aimed less at celebrating Britain than the woman who personifies it. On large screens lining the Thames, old newsreels narrated in clipped BBC English depicted the legacy of one of the longest standing and most recognizable global figures. They showed Elizabeth as a beautiful and young crown princess, standing on the balcony of Buckingham Palace alongside Winston Churchill and her father, King George VI, after a stalwart Britain had prevailed in World War II. They showed her in dignified sorrow after her father’s death, and in regal composure at her subsequent coronation. They showed her early years as a mother to four children and young wife to Prince Philip, her now 90-year-old royal consort who stood beside the queen during the 31 / 2 -hour procession on Sunday.

“Everyone is celebrating in their own way, and it is bringing people together, bringing people out into our communities, helping us to get to know our neighbors better,” Prime Minister David Cameron told reporters before being forced to move his party at Downing Street indoors because of the weather. “So there is a real purpose to this whole weekend of celebration.”

The river pageant, the largest on the Thames since one was held for the pleasure of King Charles II and Queen Catherine of Braganza in 1662, was widely seen here as a once-in-a-lifetime event. It was beamed live to a global audience and watched widely in commonwealth nations from Australia to Canada where the queen remains the official head of state.

The array of vessels ranged from one-man kayaks to Gloriana, a $1.6 million, 94-foot row barge powered by former British Olympians. Havengore, the vessel that carried Churchill’s body along the Thames for his state funeral in 1965, chugged along reverently. Another particularly poignant moment came from an assemblage of historic boats that ferried British soldiers away from advancing Nazis at Dunkirk in 1940.

Yet the biggest cry went up for the Spirit of Chartwell, a boat lent to the queen for the event and refitted with tons of gilt, flowers and two thrones. Atop the barge, the queen seemed animated, amused and, at times, touched by the outpouring in her honor.

“I look up to her because she has seen so much, survived all the scandals with her children, and come through it as someone who is more worthy of respect than anyone I know,” said Elizabeth Ewens, 19, who traveled from Oxford to see the pageant. “She’s just amazing, isn’t she? We can always count on her to be at her best for us, so I came to let her know that we’re here for her, too.”