(Corrects spelling of Westminster Abbey in dateline)
By Rachel Armstrong
WESTMINSTER ABBEY, London (Reuters) - The explosive crescendo of "Zadok the Priest", Handel's soaring anthem composed nearly 300 years ago for the crowning of King George III, marked the most sacred moment of Charles' coronation on Saturday.
Inside Westminster Abbey, where kings and queens have been crowned since 1066, around 2,200 people were there to witness Charles's robe of state be removed, before he was shielded and anointed with holy oil, then re-emerging as the choir sang "May the king live for ever".
Minutes later, after Charles was crowned and enthroned, the congregation loudly repeated the same words at the end of a pledge of allegiance to the new monarch, with the refrain echoing round the medieval building before a rousing brass fanfare began.
Until the crowning in 1953 of Charles's mother, Queen Elizabeth II, the coronations of kings and queens were seen only by those in the abbey.
Elizabeth's coronation was the first to be televised, and 70 years later video technology meant people watching on television and online around the world had better close-up views than almost everyone there in person.
Yet elements of the ceremony, which was a largely solemn and ritualistic service with just dashes of modernity, remained distinctly intimate for those inside the abbey.
The music, a mixture of centuries-old anthems written for Charles's ancestors and pieces commissioned for the occasion, ranged between unrestrained pomp to quieter choral works that reverberated around the abbey's vaulted ceilings.
Charles himself looked occasionally meek, as when he knelt before the altar with four members of the clergy surrounding him. The king's son, William, kissed his father after swearing allegiance to him.
The king, 74, also looked sometimes slightly tired and under strain.
Yet there was a snatched smile between Charles and the Archbishop of Canterbury Justin Welby as the clergyman momentarily struggled to ensure the 360-year-old St Edward's Crown was securely on the king's head.
His 9-year-old grandson Prince George sparked muffled laughter as he was shown on screens pulling funny faces shortly after his grandfather was crowned.
STATE AND CHURCH
Before Charles's arrival, representatives of nine non-Christian faith groups processed through the abbey, in keeping with the king's commitment to safeguarding religious freedom.
But the ceremony itself was deeply Christian, centred on Charles's oath to serve God as well as the people of Britain and 14 Commonwealth realms where he is head of state.
He was flanked at every moment by senior members of the clergy, while each stage of the service showed just how closely Britain's monarchy is bound and underpinned by the Church of England.
"The weight of the task given to you today, your majesties, is only bearable by the Spirit of God," Welby said in his sermon as he addressed Charles and the new Queen Camilla.
Some historians may question whether future coronations can retain the same deep Christian structure as church attendance in Britain continues to decline.
But the sense of occasion and historic rituals that - because the last coronation was 70 years ago - few people in Britain have witnessed before were likely enough to captivate almost all those who watched it.
(This story has been refiled to correct the spelling of Westminster Abbey in the dateline)