LONDON >> An elegant, tiara-bedecked Kate Middleton swept down the aisle to marry Prince William at Westminster Abbey as royal fans packed the streets of London, hoping to snatch a glimpse of a historic royal wedding expected to revitalize British monarchy.

Some 2 billion people across the globe were expected to tune in as the future king and queen of England start their lives as husband and wife with the two simple words “I will.”

A million well-wishers — as well as some protesters — flooded into the areas surrounding Buckingham Palace, Westminster Abbey and other London landmarks. Crowds were up at dawn waving flags for television cameras under steely gray skies and cool temperatures. Cheers erupted as huge television screens began broadcasting at Trafalgar Square and Hyde Park.

“Will, it’s not too late!” said one sign held aloft by an admirer dressed as a bride.

Middleton’s ivory wedding gown, with lace applique, was designed by Sarah Burton at Alexander McQueen, while her hair was half up, half down and decorated with a tiara. William wore the scarlet tunic of an Irish Guards officer, sending a strong signal of support for the armed forces and reinforcing his new image as a dedicated military man.

Maid of honor Pippa Middleton arrived in a simple column dress, and naturally styled hair, while best man Prince Harry wore formal military attire. The flower girls also wore cream dresses with full skirts and flowers in their hair.

In contrast to the clamor outside, inside the abbey all was airy and calm. The long aisle leading to the altar was lined with maple and hornbeam trees as light streamed in through the high arched windows.

Plumage of Amazonian variety filled the cavernous abbey as some 1,900 guests filed in, the vast majority of women in hats, some a full two feet (.6 meters) across or high. Some looked like dinner plates. One woman wore a bright red fascinator that resembled a flame licking her cheek. A BBC commentator noted there were some “very odd choices” in fashion walking through the abbey door.

Most men, however, looked elegant and suave in long tails, some highlighted by formal plaid pants and vests. Others wore military uniforms.

All the clamoring over every detail — the wedding dress, her hair, their titles, the romantic kiss on the balcony, the honeymoon — is finally being answered. But the biggest question won’t be resolved for years: Will this royal couple live happily ever after?

Will their union endure like that of William’s grandparents — Queen Elizabeth II and Prince Philip, now in its 64th year — or crumble in a spectacular and mortifying fashion like that of his own parents, Prince Charles and Princess Diana?

Recent history augurs badly: The first marriages of three of the queen’s four children ended in divorce. But William and Kate seem to glow with happiness in each other’s company, and unlike Charles and Diana they’ve had eight years to figure out that they want to be together.

Still, the fate of their marriage depends on private matters impossible for the public to gauge. Any wedding is fundamentally about two people. Will their lives together, starting with such high hopes, be blessed by good fortune, children, good health, productive work?

Much will depend on whether 28-year-old William and 29-year-old Kate can summon the things every couple needs: patience, love, wit and wisdom. But they face the twin burdens of fame and scrutiny. Money, power, beauty — it can all go wrong if not carefully nurtured.

These are the thorny issues upon which the fate of the monarchy rests, as the remarkable queen, now 85, inevitably ages and declines.

Brenda Hunt-Stevenson, a 56-year-old retired teacher from Newfoundland, Canada, said there was only one thing on her mind. “I want to see that kiss on that balcony. That’s going to clinch it for me. I don’t care what Kate wears. She is beautiful anyway.”