The outsize genius of Grigory the Great

<i>Prince of Princes: the life of Potemkin </i>by Simon Sebag Montefiore (Weidenfeld &amp; Nicolson, &pound;25, 634pp)

On the night of 28 June 1762, the newly-acclaimed Catherine II of Russia appeared at the door of the Winter Palace, dressed in a borrowed army uniform. Catherine took the reins of her horse, Brilliant, and was handed her sword, but realised she had forgotten to attach a dragonne, or sword-knot.

On the night of 28 June 1762, the newly-acclaimed Catherine II of Russia appeared at the door of the Winter Palace, dressed in a borrowed army uniform. Catherine took the reins of her horse, Brilliant, and was handed her sword, but realised she had forgotten to attach a dragonne, or sword-knot.

This was noticed by a sharp-eyed guardsmen, who galloped over to her across the square, tore the dragonne off his own sword and handed it to her with a bow. His name was Grigory Potemkin. He was a man of almost giant stature with looks that had won the nickname of "Alcibiades". He had a definite talent for seizing the moment.

The 18th century, on the cusp as it was between the religious past and the scientific future, had a talent for producing individuals who combined to an excessive degree opposing characteristics - licentiousness and intellectual brilliance, sloth and ambition, superstition and rationalism. Prince Potemkin was the supreme example. The Prince de Ligne described him as "the most extraordinary man I ever met... what is the secret of his magic? Genius, genius, and more genius".

Yet, in our age Potemkin's name means little, or only largely spurious things: phoney villages, built to please his royal paramour for whom his real task was that of sexual athlete, and a mutiny on the battleship Potemkin in 1905. Fortunately, in Simon Sebag Montefiore, Potemkin has a biographer who has restored him to his rightful place in history, telling the heroic and mesmerising tale of a statesman with superhuman gifts, and a man whose coruscating wit was balanced by tender emotions.

Prince of Princes is an account of one of the greatest love stories of modern history: the mating of two eagles, whose mutual passion and affection placed Anthony and Cleopatra in the second league.

Potemkin was born in 1739, into a penurious aristocratic family from Smolensk. In 1761, having been thrown out of university for dissipation, he joined the Horse Guards in St Petersburg. Remarkably handsome, with a seductive humour, he soon impressed the women of the capital.

After the death of Empress Elizabeth, a conspiracy arose to depose her mentally feeble successor Peter III and replace him with his wife, the German-born Catherine. The story of the coup has been told before, most cavalierly in the Hollywood film The Scarlet Empress, in which Catherine was played by a young Marlene Dietrich. In Sebag Montefiore's hands, it takes on an immediacy in the resplendent narrative tradition of Macaulay and Trevelyan. The events of history rush up from the page.

Catherine, whose political success owed much to her handling of men, was described as having "the soul of Caesar and the seductions of Cleopatra". Out of all her admirers, she soon came to prefer Potemkin, her junior by ten years. Her letters reveal a girlish lack of formality. She called him "Grishenka" and "Lion of the Jungle" - perhaps a reference to his sexual prowess. She waited for two hours outside his room, too shy to go in. He, in turn, called her "Matushka" or Little Mother.

Potemkin became virtual co-ruler of the empire, a fact to which contemporaries paid heed. Legend had it that there was a secret marriage; the author would seem to support this. Certainly, Catherine began to refer to Potemkin in her letters as "husband". Their sexual affair probably lasted only a few years but his influence continued to grow.

Raised to prince, he took every opportunity to familiarise himself with European politics. He was convinced that Russian expansion should be aimed southwards to secure the Crimea, Black Sea and Caucasus; in 1782, he annexed the Tartar Khanate of the Crimea. In the south he built not phoney villages of pasteboard, as his enemies pretended, but important cities including Odessa and Sebastapol. He created the Black Sea fleet, for which Catherine made him governor-general of New Russia. The apogee of his public life was victory in the second Russo-Turkish war.

Scandal dogged Catherine and Potemkin, especially over the latter's affairs with three of his young nieces, ladies of the empress's bedchamber. That Catherine continued to love him is not in doubt, however.

The contradictions in Potemkin's character are beautifully brought out in this magnificent biography. He loved riches and pomp, yet often wandered around naked under an open bearskin dressing-gown, chewing his nails. He felt compelled to have sex yet could exhibit a monk-like piety. He lived on gold yet died on the grass. In 1791, exhausted by hard living, Potemkin collapsed out in the steppe and expired in the arms of one of his nieces. His death is one of the great set- pieces in this important book.

Catherine never recovered from his loss. When great men died, their viscera were buried separately. Potemkin's bones were interred in the Ukraine, his innards found their way to present-day Romania, but his heart rests in Russia. As the poet Derzhavin wrote in tribute, "Roar on, roar on, O waterfall".