At noon on Friday, the Sebastopol bell at Windsor rang 96 times, marking each year of Queen Elizabeth II's life.
The last time the bell, captured in Crimea in 1856, was heard was at the funeral of her mother, the last Empress of India, in 2002. Weighing nearly a ton and taken from the Church of the Twelve Apostles in Sevastopol, it hangs in the Round Tower.
It tolls only for the deaths of the most senior royals. In 1952, it rang 56 times to mark the life of George VI, Queen Elizabeth's father. The same tradition was marked in 1910 and 1936, marking the arrival of the royal coffin at Windsor.
It was a highly symbolic moment in the ceremonies that accompany the death of a British monarch.
The King has announced that the Royal family and household have entered a period of court mourning that will last until seven days after the late Queen's funeral.
The Royal family will wear dark colours and engagements will not take place unless the King himself authorises them. Official documents will be printed with a black edge. Under national mourning, flags other than the Royal Standard will be flown at half-mast.
Mourning is a tradition steeped in history, but also a very flexible one. At its height, under Queen Victoria, it was taken to excess. On the death of her husband, Prince Albert, in 1861, she ordered that it last "for the longest term in modern times". Members of the family were not seen for a year.
The public followed suit, embracing black clothing and decorations, and Victoria helped to create stringent social attitudes to mourning that would last well into the following century.
However, when she refused to end her mourning, continuing to wear black and avoiding public life until her death four decades later, it led to a spike in republican sentiment.
After her death, the period of mourning lasted a full year. When the then Duke and Duchess of Cornwall, the future George V and his wife, went on an imperial tour two months later in January 1901, they wore mourning clothes throughout.
Every contingency was made so that the Duchess could wear black or dark grey, no matter the climate. For tropical wear, she had a grey, unlined cashmere dress, while the Duke had plenty of black frock coats packed for him.
As public sentiment towards grieving has softened, so too has the Royal family's approach. The death of George V in 1936 was marked by six months of mourning, while that for the death of George VI in 1952 was 16 weeks.
Royal mourning is not, however, restricted to the deaths of monarchs. It has been declared for various members of the family, including the Queen Mother, and also for overseas royalty.
In January 1953, the Queen announced seven days of royal mourning following the death of the Danish queen mother, Queen Alexandrine, although this did not impact the public. On such occasions, a lower level of mourning is usually declared, known as family rather than court mourning.
Whatever the level, it is up to the monarch of the day to decide what is or is not appropriate. When Princess Margaret died, Queen Elizabeth carried on with her duties. Buckingham Palace said it was what the Princess "would have wanted".
When the Queen Mother died weeks later, however, Queen Elizabeth chose to reduce all but her charitable engagements.
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