Queen Elizabeth II marks another milestone
As Queen Elizabeth II enters the history books as Britain's second longest-reigning monarch, BBC royal correspondent Nicholas Witchell looks at how her 59-year reign compares with those of other long-serving sovereigns.
Last month the Queen celebrated her 85th birthday. Next year she will reach her Diamond Jubilee, when it will be 60 years since she came to the throne.
Elizabeth II has achieved a number of significant milestones as Queen of the United Kingdom, and this week she passes another.
On Thursday 12 May 2011, she becomes the second-longest serving monarch Britain has ever had.
On that day she overtakes the length of the reign of George III, a king remembered largely for the "madness" which overtook him in later years.
George III died in 1820 after a reign lasting 59 years and 96 days.
Now the reign of Elizabeth II (or Elizabeth I in Scotland, since the crowns of England and Scotland were only brought together in 1603, after the reign of the other female monarch called Elizabeth) is surpassed in length by that of only one other British sovereign.
Who else, of course, but Queen Victoria, who reigned for 63 years, seven months and three days, and died at the age of 81 in January 1901.
Victoria's reign witnessed Britain's rise to become the then-global superpower. There were industrial, cultural and scientific changes on an unprecedented scale and by the time of her death the British Empire encircled the globe.
George III's reign was also a period of great change for Britain. The American colonies may have been lost during his time on the throne, but the military ambitions of France were decisively defeated at the battles of Trafalgar and Waterloo.
George III was also, incidentally, the first king of the entity known as "the United Kingdom" after the union of the crowns of Great Britain and Ireland in 1801.
But neither reign can surely quite match the sheer scope of the changes that have occurred during the reign of the present Queen.
She came to the throne less than seven years after the end of World War II. Britain was victorious but essentially bankrupt. Sir Winston Churchill was prime minister and food was still rationed.
In the years that have followed Britain has shed its empire and seen changes to virtually every significant aspect of national life that could scarcely have been imagined on that February day in 1952 when she was so suddenly propelled onto the throne by the death of her father, George VI.
No let up
The one constant presence on the national stage throughout the past six decades has been the Queen. Today, the majority of the British population (to say nothing of the inhabitants of the 15 other "realms" of which she is also sovereign) have known no other head of state.
She will never retire. Only at the moment of her death will she cease to be Britain's Queen. Even if she were to become incapacitated, she would still remain monarch, albeit then with her immediate heir taking over her constitutional duties as Prince Regent (exactly as happened in the final years of the reign of George III).
But there is not the slightest sign that the reign of Elizabeth II is slowing down in any significant way.
Next week she will make an historic first state visit to the Republic of Ireland, the territory that was once part of the British Crown; later this year she will travel once again to another of "her" countries, Australia, for a meeting of Commonwealth heads of government, and next year she will visit different parts of the UK to celebrate her jubilee.
Will she beat Queen Victoria's record?
If Elizabeth II is still on the throne on 10 September 2015 she will have done so. She will then, metaphorically speaking, be crowned as the longest-serving sovereign in the 1,000 year history of the British monarchy.
Few at the moment could possibly doubt that she will do it.