Hundreds of thousands of people are in central London for today’s wedding of Prince William and Kate Middleton, after some camped out overnight along the route the newlyweds will take in a carriage procession.

Local officials estimate the flag-waving crowd will swell to 600,000 people. William arrived at Westminster Abbey about 40 minutes before the ceremony was due to start at 11 a.m. As many as 5,000 people stayed on the streets overnight, the BBC reported. The weather is dry, though forecasters say there may be showers later. The U.K. government says the event will be seen by 2 billion people on television around the world. It’s a public holiday throughout Britain.

“We got a few hours sleep, on and off,” said Sheila Barton, 57, who started camping on The Mall at 5 p.m. yesterday after traveling from Sevenoaks, southeast of London. “We kept warm with layers, food, drink and cuddling up. We chose this spot so we have a good place to run into the park when they drive past.”

Middleton is the first woman from outside royalty or the aristocracy to marry so close to the throne for 350 years. When William becomes Britain’s monarch, she will be queen. Queen Elizabeth II, William’s grandmother, announced today that the couple will be known as the Duke and Duchess of Cambridge after their wedding.

Posh and Becks

Among those arriving early for the ceremony were soccer player David Beckham and his wife Victoria, and Elton John, who sang at Diana’s funeral. Also invited are more than 40 foreign royals such as Queen Margrethe of Denmark.

Today’s celebrations are the U.K.’s biggest royal event since the funeral in 1997 of William’s mother, Diana, who died in a car crash in Paris after her marriage with Prince Charles ended in divorce.

“Like many people my age I’ve watched Prince William grow up and all the challenges he has had, including losing his mother, but now finding love and wanting to get married,” Prime Minister David Cameron told reporters before heading to the abbey. “Like anyone who has lived in Britain, I feel quite an attachment to this whole event and that is why I think the whole country is getting so excited about it.”

No Repeat

Charles and Diana married at St. Paul’s Cathedral in the City of London in 1981. That event was “incredibly lavish and extravagant” and isn’t being replicated today, according to Hugo Vickers, the author of “Elizabeth, The Queen Mother,” a biography of William’s great-grandmother and an adviser on the Oscar-winning movie, “The King’s Speech.”

“This is actually a more traditional royal wedding — the Queen and Prince Philip were married at Westminster Abbey along with other royal couples,” Vickers said in a telephone interview. “You could argue that the archbishop at Charles and Diana’s wedding saying ’this is the stuff of which fairy tales are made’ put too much of a burden onto that couple.”

Middleton, 29, spent her last night as an unmarried woman in the 111-year-old Goring Hotel. Her day is mapped out with military precision. While getting dressed, the princess-to-be will hear the sound of military marching bands across London.

She will travel from the hotel by car, in the company of her father, Michael, at 10:51 a.m. and arrive at Westminster Abbey at exactly 11 a.m.

Waiting for Dress

That’s the moment when the public will have its first view of the bride’s dress, whose design — and the name of the designer — has been kept secret.

“I want to see her dress, it’s going to be lush,” said Kiayra Mansfield, 18, from Lloydminster, Alberta.

When Diana Spencer, then aged 20, married Prince Charles in 1981, she wore an ivory taffeta and antique lace dress with a 25-foot train and puffed sleeves, designed by Elizabeth Emanuel.

Middleton will be attended today by five bridesmaids including her sister, Pippa, and two pageboys. They arrive at the abbey at 10:55 a.m.

The groom was accompanied to the abbey by his best man and younger brother, Prince Harry.

William, 28, who as monarch will command Britain’s military, is dressed in the uniform of a colonel of the Irish Guards regiment, his senior honorary appointment in the army. He is currently a flight lieutenant in the Royal Air Force, based in north Wales, and could also have worn a naval uniform. Harry, 26, is wearing the uniform of a captain of the Household Cavalry.

Queen’s Arrival

The most important guest, the queen, will be the last to get to the abbey at 10:45 a.m.

During the four minutes it takes Middleton to walk down the aisle at the abbey, she will pass floral decorations that include eight 20-foot trees alongside blossoms, azaleas, rhododendron, beech, wisteria and lilac.

The 1,000-year-old abbey has hosted 15 royal weddings. The service will be conducted by the Dean of Westminster, John Hall, and the Bishop of London, Richard Chartres, and the wedding ceremony itself by the senior cleric in the Church of England, the Archbishop of Canterbury, Rowan Williams.

When the couple exchange vows, Middleton will be given a gold wedding ring to wear alongside her sapphire and diamond engagement ring. The ring was made by a family-owned London- based jeweler, Wartski, from a piece of Welsh gold given to William by the queen after the engagement was announced last year.

Open Carriage

Following the ceremony the newly married couple will leave the abbey at 12:15 p.m. in an open-air state landau carriage, the same vehicle used by Charles and Diana 30 years ago, along a union flag-lined route to Buckingham Palace. If it’s raining heavily, a covered carriage known as the Glass Coach will be used for the 15-minute journey.

The couple will have their photographs taken inside the palace before emerging on to the balcony at 1:25 p.m. to wave to the crowds and, perhaps, to kiss in public as man and wife for the first time.

A flypast of three planes from World War II symbolizing the Battle of Britain — a Spitfire, a Lancaster and a Hurricane — alongside four modern jets — two Tornados and two Typhoons — will salute the newlyweds.

“In our era, we always hear about the past, stories of kings. This will be part of our history, in 50, 100 years’ time, so it’ll be great to be able to tell my grandchildren I was here,” said Marcelo Ros Castilho, 27, an IT project manager from Sao Paulo, Brazil. He camped out on The Mall with friends and family.

Two Cakes

After the air display, around 650 people will attend a lunchtime canape reception at the palace. Two cakes will be cut. One is a multi-tiered fruit cake decorated with white icing and flowers and the other a chocolate cookie cake made from a royal family recipe.

In the evening, there will be a 300-strong reception at the palace for the couple’s close friends with dinner and dancing. That’s where Prince Harry will make his best man’s speech. Where the couple will travel on honeymoon is another secret.

The ceremony, the lunch and the evening dinner will be paid for by Charles and the queen, while Kate’s parents, self-made millionaires who run their own company, Party Pieces, are also contributing.

By the end of the day, Middleton’s life will have changed utterly.

“She will one day, as the queen is, be a figurehead for this country,” Claudia Joseph, author of “Kate: The Making of a Princess,” said in a telephone interview. “In one sense it will be extremely restrictive and limiting but she will also have experiences that other people can only dream of.”