The Queen is about to become the longest-serving sovereign in our history: on September 9 she will surpass Victoria’s record of 63 years and 216 days on the throne.

Prompted in part by this anniversary, I have spent the last year writing brief lives of all 40 monarchs from 1066 to the present day. The resulting book, called Gimson’s Kings and Queens and beautifully illustrated by Martin Rowson, has just appeared.

My hope was to entertain, not to instruct. But I couldn’t help wondering, as I made my way from William the Conqueror to Elizabeth II, about the nature of monarchy itself.

A year is not long enough to develop a grand theory about this: in all likelihood, a lifetime would not be enough, and the theory would be wrong. Our greatest writer about kings and queens, William Shakespeare, was a poet and dramatist rather than a theorist. And if one must try to analyse the secrets of our constitution, the description of things as they actually are (attempted most memorably by Bagehot) is preferable to pieties about how they ought to be.

But here are eleven points that struck me:

1. We are extraordinarily ignorant about the nature of monarchy. Writers about politics are interested in power. For most of the time, they concentrate on democracy and ignore the monarchy, in part because the Queen is said to be “above politics”, and to have no power.

2. There is nevertheless great interest in the House of Windsor: greater than in almost all politicians. The monarchy has something (but what exactly?) which democratic politicians lack. According to Bagehot, “A family on the throne is an interesting idea… It brings down the pride of sovereignty to the level of petty life.”

3. Most of the writing about the Queen is unilluminating. To avoid veering into excessive deference, or else into the contempt shown by some writers of comedy programmes for Radio Four, is difficult. And some essential aspects of her, including her Christian faith, are almost entirely ignored.

4. According to Max Weber, “In the evolution of political charisma, kingship represents a particularly important case in the historical development of the charismatic legitimisation of institutions. The king is everywhere primarily a war lord, and kingship evolves from charismatic heroism.”

5. Until the eighteenth century, our kings and queens very often stood or fell according to their success as war leaders. Even in the 20th century, if we had lost a world war, the chances of this country becoming a republic would have been very much higher. George II was our last monarch to lead his soldiers into battle, at Dettingen in 1743. But the future George VI served at the Battle of Jutland in 1916, and the connection with the armed forces has remained very close.

6. Our greatest monarch, Elizabeth I, was a great war leader, whose speech at Tilbury in 1588, defying the Spanish invasion threat, is the most stirring by any English monarch. Richard III lost his throne, and his life, at Bosworth Field in 1485 because his numerically superior force refused to fight for him. William III, our most underestimated king, was a formidable military commander as well as a great statesman: but for him, the Glorious Revolution of 1688 would almost certainly not have been glorious.

7. But it is not just a question of war. Kings who overplayed their hands, and misjudged the temper of their people, for example by imposing a form of religion to which the public were averse, tended to come to a bad end: Charles I, beheaded in 1649, and James II, chased out just under 40 years later, are examples of that. So are Edward II, overthrown in 1327, and Richard II, who by 1399 had become unbearable. So in his own way was Edward VIII in 1936: he wouldn’t conform to what either the establishment or the public wanted, so off he went.

8. So although we think of monarchs as powerful figures, they have always been constrained by what their contemporaries find acceptable. Henry VIII broke with Rome in the early 1530s because he wished to marry a younger woman, but in order to make a success of this outrageous manoeuvre, he mobilised widespread anti-clericalism, and turned Parliament into his enthusiastic junior partner.

9. The present Queen’s success derives in part from her evident determination never to overplay her hand. Her respect not only for constitutional practice, but for the people she meets, makes it difficult not to respect her. Her authority springs from her acknowledged powerlessness.

10. Our kings and queens are in their different ways a wonderfully amusing set of people, struggling to perform a role which still exercises, for reasons which stretch far back into our history and are not entirely clear, an irresistible hold on the human imagination.

11.  How the preachers of democratic pieties (who are themselves most often – not that they like to admit this –  of an oligarchic outlook) shudder when they detect the return of hereditary characteristics to supposedly republican governments: the emergence, say, of another Bush or Clinton. But the urge to pass abilities and possessions on to our descendants is part of human nature. Perhaps that is one reason why kingship, grandest expression of the hereditary principle, still speaks even to those of us who are determined to close our ears to it.

Gimson’s Kings and Queens: Brief Lives of the Monarchs since 1066 is published by Square Peg (£10.99).