Books: More books than bastards, more battles than both

King Frederick II of Prussia was revered by the Nazis as the "father" of modern Germany. Certainly his long and largely successful wars against Austria - thereby setting in train a century-long struggle for dominance in Germany which ended with Prussia's decisive victory at the Battle of Koniggratz in 1866 - laid the foundation stone for the unified German state. But the creation of a united Germany was never his intention, for he was a Prussian patriot who had no concept of German nationalism.

Born in Potsdam in 1712, the clever but melancholic young prince was encouraged in his intellectual and artistic pursuits - he was a keen musician and well acquainted with the works of Descartes, Bayle and Locke at 15 - by his culture-loving mother, Sophia Dorothea of Hanover (the sister of our own George II). But his austere and militaristic father, King Frederick William I, despised such "effeminate" pursuits and frequently used violent language and deeds to bend his unruly son to his puritanical will. The feuding came to a head in 1730 when the 18-year-old Frederick's attempt to defect to France was foiled and he was imprisoned in the fortress of Kstrin. Worse still, he was forced to witness the beheading of his friend and accomplice, lieutenant Hans von Katte.

Three years later, by now partially reconciled to his father, Frederick grudgingly agreed to marry Elisabeth of Brunswick-Bevern, the daughter of a minor German prince. According to society gossip, the King had to threaten and cajole his son into the marriage bed; and even then he only remained for an hour. They never had children, probably because Frederick was homosexual and found conventional sex distasteful. MacDonogh certainly hints at the possibility, though he also suggests that Frederick's sexual organs may have been "physically underdeveloped" and dutifully lists a number of women with whom the young prince was suspected of having affairs.

On the credit side of marriage, however, was the provision of a separate establishment at Rheinsberg near Berlin where, in the final years of his father's reign, Frederick was at last able to indulge his higher calling by reading voraciously and corresponding with the (mainly French) leading lights of the Enlightenment, including the philosopher Maupertais and the poet Voltaire. No sooner had he succeeded his father in 1740 than he instituted an academy of arts and authorised the building of an opera house. He also restricted the use of torture and abolished the practice of sacken, whereby female child murderers were sewn into leather sacks and drowned.

Yet, as the author rightly points out, there were "no signs of pacifism in the new king". Instead he wasted little time strengthening his army and invading Austrian Silesia, a rich, fertile province that paid a quarter of the total tax bill for all Habsburg lands. His reputation was hardly enhanced at the subsequent battle of Mollwitz, when he panicked and fled the field before his generals managed to pluck victory from the jaws of defeat. A second hard-fought victory over the Austrians a year later (as the First Silesian War merged into the War of the Austrian Succession) did him more credit in that, in MacDonogh's words, he "stayed to the end this time". For all Frederick's pacifist claims that a strong army was necessary to protect the peacetime cultivation of the arts, one gets the impression that he enjoyed war and the repute that it brought him. After yet another success over the Austrians (and the Saxons to boot) at Hohenfriedberg in 1745, he told a family friend that the "Romans had never achieved anything so brilliant". Of course there were defeats - notably at Kolin and Kunersdorf during the Seven Years' War - but he will always be remembered for the odds-defying victories of Rossbach and Leuthen during the same conflict when Prussia was facing annihilation by a coalition of hostile powers (including Russia, Austria and France). Nevertheless, it required the accession of the Prussophile Tsar Peter III of Russia in 1762 to save Frederick from ultimate defeat. His remaining years were largely peaceful - apart from a brief spat with Austria in 1778-9 - and were spent rebuilding his shattered provinces (which he achieved with notable success), reforming the Prussian legal system (another success), and putting down "his reflections on virtually every subject that sprang to mind, practical and philosophical". His Testament Politique, for example, which was addressed to his nephew and successor, stated that it was no longer possible for a king just to administer justice; for he needed to keep an eye on it and make sure that everybody obeyed the law, including himself.

But Frederick's enlightened despotism had its limits: he expounded religious toleration, yet was still capable of warning his successor that Prussia had "too many Jews in the towns"; his intention to abolish serfdom was watered down because of opposition from his beloved nobles; and it was he who initiated the cynical partition of Poland in 1772 (thereby acquiring the province of West or Polish Prussia).

Macdonogh's account of Frederick the Great's extraordinary life may rely entirely on published sources (many of them French), but is no less colourful or compelling for that. Elegantly written and scrupulously fair, it successfully manages to capture the essence of this warrior-philosopher king in all its contradictory detail. The last word is left to Voltaire. Frederick "has written more books than any of his contemporary princes has sired bastards", he wrote in 1772, "and he has won more victories than he has written books".