Queen Elizabeth's coffin has been made following a Royal tradition that makes such distinguished burial caskets a heavy load for the members of the Armed Forces in the bearer parties who have carried Her Majesty with pride and respect on her final journey around the UK.
Made 30 years ago out of English oak and lined with lead, the coffin is estimated to weigh at least 550lbs, or a quarter of a tonne, and anywhere up to 700lbs.
A precise weight might not be known publicly, but a rough estimate can be made based on the weight of lead, the oak outer casket and based on what is known about previous Royal caskets made with similar features and in a similar tradition.
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Brass fittings and other attachments upon which to fix Royal regalia, such as the Royal crown, would add to the weight of the seasoned oak casket.
If compared to, say, a bergen on a standard British Army fitness test, which weighs up to about 25kg (55lbs), that means the coffin could weigh the equivalent of up to 12 bergens, or up to eight fully-laden bergens that might weigh in at 80lbs each on an exercise.
Her Majesty's coffin has so far been carried by a bearer party of eight pallbearers from the Royal Regiment of Scotland and The King's Body Guard for Scotland, who carried the late Queen into St Giles's Cathedral in Edinburgh, while a bearer party from the Royal Air Force was raised to convey her coffin onto the aircraft at Edinburgh Airport for her journey to London.
A bearer party from the Queen's Colour Squadron (63 Squadron RAF Regiment) carried Her Majesty from RAF Northolt into the state hearse for her journey to Buckingham Palace on Tuesday evening.
Details of which regiment will form the bearer party for Her Majesty's final journey into Westminster Abbey have not yet been made public.
The heavy weight of a Royal coffin is not uncommon in state funerals in Britain or around the world, nor with some military funerals such as in the US where many caskets are made out of 18 gauge steel.
Members of the Armed Forces, both in Britain and in other nation states, rehearse and practice for such sombre occasions to ensure the deceased's final journey is carried out with dignity.
In America, for instance, an elite unit of Company B of the United States Marine Corps. known as the Body Bearer Section, trains "to carry their own" to their final resting place at Arlington National Cemetery, and the caskets they lift can weigh up to 800lbs, or about 57 stone.
Her Majesty's casket was made more than three decades ago by a funeral company that is no longer in business, meaning some of the finer, public details of its manufacture are lost in the mists of time.
However, the coffin follows many of the traditions of a Royal casket and with that, many of the features are in keeping with the caskets of other late members of the Royal Family, including that of the Duke of Edinburgh, whose casket was also lined with lead and made by the same company that made the Queen's coffin.
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Why are Royal coffins lined with lead?
Royal coffins are lead-lined, creating a lead casket inside the oak coffin, to help preserve the body for longer in an airtight seal while the deceased is lying in state and for when they are laid to rest above ground.
In the case of Her Majesty's final resting place, she will be interred at the King George VI Memorial Vault alongside her late husband Prince Philip, and other late members of her family including her father King George VI, her mother Queen Elizabeth The Queen Mother, and sister Princess Margaret.
The vault is at St George's Chapel in the grounds of Windsor Castle, which has been the final resting place for members of the Royal Family since the 15th Century.
As with the Queen and the Duke of Edinburgh's coffins, Princess Diana's casket was also known to have been lined with lead, and reports at the time of her funeral in 1997 suggested her casket weighed up to 700lbs, or 50 stone.
Royal regalia adorns the coffin
The Queen's coffin, adding to the weight, is also fitted with brass handles and other fitments, including fastenings to attach the Imperial State Crown, the sovereign's Orb, a golden globe that dates back to 1661 which is symbolic of the monarch's power derived from God, and the sovereign's Sceptre featuring a cross which was also presented at her coronation and which has been part of every coronation since Charles II in 1661.
Specialist funeral directors Henry Smith, which went out of business 17 years ago and also made the Duke of Edinburgh's casket, is reported to have made the Queen's coffin before maintenance of the casket was then said to have passed to funeral directors JH Kenyon Ltd of London.
North London-based company Leverton and Sons was put in charge of Royal funerals in the early 1990s.
Andrew Leverton, who manages the family business, told the Times newspaper in 2018 that the Queen's coffin had been ready for decades, adding: "It is made from English oak, which is very difficult to get hold of. Oak coffins are now made from American oak.
"I don't think we could use English oak for a coffin now. It would be too expensive."
Few details of the original manufacture are said to have passed through the companies and while it is known that the wood for Royal coffins is traditionally sourced from oak at the Sandringham estate, such specific details are no longer in the public domain regarding the Queen's casket.
Lying In State
The Queen's coffin will rest in Westminster Hall in London from Wednesday, where Her Majesty will lie in state until the coffin is moved from the Houses of Parliament to the neighbouring Westminster Abbey for her funeral on Monday, 19 September.
Her Majesty's coffin is expected to be rested on a raised platform called a catafalque – a decorated framework that supports the coffin – while lying in state and will be draped in a Royal flag, likely to be the Queen's own personal standard.
Her Majesty will be flanked by a loyal guard from the Armed Forces at all hours of the day and night.
The Royal crown and other regalia of the late sovereign is normally placed on top of the coffin as she is rested, while a guard, by units from the Sovereign’s Bodyguard, the Household Division or Yeoman Warders of the Tower of London, will stand watch at all hours.
King Charles III and senior members of the Royal Family, along with members of the Armed Forces, will escort the Queen's coffin for her final journey while hundreds of thousands of people are expected to line the streets as they mourn and pay their final respects.