By Michael Holden, Andrew MacAskill and Paul Sandle
LONDON (Reuters) - King Charles III arrived at London's Westminster Abbey on Saturday to be crowned in Britain's biggest ceremonial event for seven decades, a sumptuous display of pageantry dating back 1,000 years.
Charles succeeded his mother Queen Elizabeth when she died last September and at 74, he will become the oldest British monarch to have the 360-year-old St Edward's Crown placed on his head as he sits upon a 14th century throne at London's Westminster Abbey.
The king and his second wife Camilla, 75, who will be crowned queen during the two-hour ceremony, left Buckingham Palace in the modern, black Diamond State Jubilee Coach accompanied by cavalrymen wearing shining breastplates and plumed helmets.
In the abbey, watched by about 100 heads of state and dignitaries, including U.S. first lady Jill Biden, and millions on television, Charles be crowned as his predecessors have been from the time of William the Conqueror in 1066.
While rooted in history, the event will also attempt to present a forward-looking monarchy.
For a nation struggling to find its way in the political maelstrom after its exit from the European Union and maintain its standing in a new world order, its supporters say the royal family still provides an international draw, a vital diplomatic tool and a means of staying on the world stage.
"No other country could put on such a dazzling display - the processions, the pageantry, the ceremonies, and street parties," Prime Minister Rishi Sunak said.
Despite Sunak's enthusiasm, the coronation is taking place amid a cost of living crisis and public scepticism, particularly among the young, about the role and relevance of the monarchy.
Saturday's event will be on a smaller scale than that staged for Queen Elizabeth in 1953, but will still aim to be spectacular, featuring an array of historical regalia from golden orbs and bejewelled swords to a sceptre holding the world's largest colourless cut diamond.
Hundreds of soldiers in bright scarlet uniforms and tall black bearskin hats lined the route along The Mall, the grand boulevard to Buckingham Palace, where tens of thousands ignored the light rain to mass in a crowd more than 20 people deep in some places.
"I saw the beautiful white horses pulling the carriage," said Beverlee Moag-Walker, 49, from Northern Ireland as the king's carriage went past. "It was fabulous."
Michelle Fawcett, 52, a barrister, said: "It was a moment in history and pretty spectacular."
However, not all were there to cheer Charles, hundreds of republicans booed and waved banners reading "Not My King".
More than 11,000 police are being deployed to stamp out any attempted disruption, and the Republic campaign group said its leader Graham Smith had been arrested along with five other protesters.
"It is disgusting and massively over the top," said Kevin John, 57, who was among the anti-monarchy protesters.
After the service, Charles and Camilla will depart in the four-tonne Gold State Coach that was built for George III, the last king of Britain's American colonies, riding back to Buckingham Palace in a one-mile procession of 4,000 military personnel from 39 nations.
It will be the largest show of its kind in Britain since the coronation of Charles' mother.
GREAT AND GOOD
Inside the abbey, bedecked with flowers and flags, politicians, and representatives from Commonwealth nations took their seats alongside charity workers and celebrities, including actors Emma Thompson, Maggie Smith, Judi Dench and U.S. singer Katy Perry.
Much of the ceremony will feature elements that Charles' forebears right back to King Edgar in 973 would recognise, officials said. Handel's coronation anthem "Zadok The Priest" will be sung as it has at every coronation since 1727.
But there will be new elements, including an anthem composed by Andrew Lloyd Webber, famed for his West End and Broadway theatre shows, and a gospel choir.
A Christian service, there will also be an "unprecedented" greeting from faith leaders and Charles's grandson Prince George and the grandchildren of Camilla will act as pages.
However, there will be no formal role for either Charles' younger son Prince Harry, after his high-profile falling out with his family, or his brother Prince Andrew, who was forced to quit royal duties because of his friendship with late U.S. financier Jeffrey Epstein, a convicted sex offender.
They sat in the third row behind other working members of the royal family.
Charles will swear oaths to govern justly and uphold the Church of England - of which he is the titular head - before the most sacred part of the ceremony when he is anointed on his hands, head and breast by Archbishop of Canterbury Justin Welby with holy oil consecrated in Jerusalem.
After Charles is presented with symbolic regalia, Welby will place the St Edward's Crown on his head and the congregation will cry "God save the King".
His eldest son and heir Prince William, 40, will pay homage, kneeling before his father and pledging his loyalty as "your liege man of life and limb".
ALLEGIANCE
Welby will call for all those in the abbey and across the nation to swear allegiance to Charles - a new element that replaces the homage traditionally sworn by senior dukes and peers of the realm.
However, that has caused controversy, with Republic calling it offensive, forcing Welby to clarify it is an invitation not a command.
After returning to Buckingham Palace, the royals will make a traditional appearance on the balcony, with a fly-past by military aircraft.
Also in traditional British fashion, the weather in London could feature heavy bursts of rain, forecasters said.
Celebrations will continue on Sunday with nationwide street parties and a concert at the king's Windsor Castle home, while volunteering projects will take place on Monday.
"When you see everyone dressed up and taking part it is just fantastic. It makes you so proud," said teacher Andy Mitchell, 63, who left his house in the early hours to get into London.
"My big concern is that younger people are losing interest in all of this and it won't be the same in the future."
(Writing by Michael Holden and Kate Holton; Additional reporting by Andrew MacAskill, Sarah Young, Suban Abdulla, Rachel Armstrong, Farouq Suleiman, Muvija M and Paul Sandle; Editing by Frances Kerry and Janet Lawrence)