They were both outsiders from islands, she from Martinique, he from Corsica. It would be hard to say who came from the less fashionable place, and their twin triumphs were in a sense even more improbable than their marriage.

Both won an equal right to claim that they embodied the revolution, and the people of Paris bestowed on her the title of “Notre Dame des Victoires”. Her grandson became Napoleon III, and as Evangeline Bruce points out in this fascinating and well documented double biography, the children she had by her first husband make her the ancestor of virtually every royal house in Europe.

She left Martinique at the age of 16 to be married to Alexandre de Beauharnais, an aristocrat whose revolutionary sympathies did not save him from being guillotined as a royalist suspect in July 1793.

She was saved from the same fate by the fall of Robespierre a year later, lived on loans and credit, captivated Bonaparte on her first meeting with him, some time in October 1795, became his mistress, married him only on the eve of his coronation on December 2, 1804, and played her role as Empress to perfection.

When it became obvious that she was not going to bear him the heir which he was convinced he needed to give his empire permanence, she accepted her divorce with dignity. She even had, as a royalist lady remarked, the good taste to die at exactly the right moment: on May 24, 1814, before Napoleon’s return from Elba gave final proof of how little his word could be trusted.

She was six years his senior, born the same year that Corsica became French and thus enabled its most famous son to be the first of the dictators - the Austrian Hitler and the Georgian Stalin are the other two - whose outsider status so exacerbated their aggressive nationalism. She was sexually experienced, and he never forgot his first night with her. He fawned on her in public in a way which would have invited ridicule in a less powerful and less hasty tempered autocrat. In the early days of their marriage, he suffered intensely from her fairly blatant infidelity with the handsome lieutenant Charles.

Miss Bruce makes it fairly clear that it was Bonaparte’s power and money which made him attractive to her, not his charm or sexual prowess.

This excellent biography nevertheless spares us the details of their physical encounters, and concentrates instead on the politics of the most dramatic period in France’s history. It does not neglect minor but fascinating aspects of Josephine’s and Bonaparte’s life such as the fact that they were ahead of their time in abandoning the aristocratic habit of having separate bedrooms to share the marital bed, anticipating what became the normal custom only in the 19th century. While Bonaparte showed a typical parvenu’s anxiety to outdo the old regime in the splendour and formality of his court, she had a more attractive simplicity of manner, and did not disdain to beat her husband - and others - at billiards.

At no point did she seek to influence his political decisions. Although she may have been a bit of a Jackie Kennedy in her attitude to money, spending the equivalent of a million dollars a year on clothes, jewellery, charities and gifts, she was no Hillary Clinton. On what became increasingly like royal progresses through France, she wore the crown jewels confiscated from the Bourbons with elegance and aplomb, but seems to have needed the opportunity to dress up to save her from the boredom of what Evangeline Bruce calls “a life of stupefying sameness entirely regulated by the Emperor, waiting for his orders and bent only on pleasing him”.

Everything might have been different if she had been able to have children by him. He was fertile with other women, and Miss Bruce credits him with two illegitimate sons in addition to his official heir, Napoleon Francois, King of Rome, the son of Marie-Ther se of Austria. The preparations for his wedding in 1810 to the niece of the executed Marie Antoinette were far more elaborate than those which had accompanied the marriage of Louis XVI in 1770, just as his self-coronation excelled in splendour anything traditionally arranged for the anointing of France’s legitimate sovereigns.

Paradoxically, the man who was arguably the greatest French warrior of all time ended his career by exposing his country to the humiliation of having its capital city occupied by foreign troops for the first time since the Middle Ages. He gave France a legal and administrative system which has changed remarkably little over almost 20 years, and stabilised the franc at a value which it maintained until 1918.

But Miss Bruce reminds us that at least three million people died as a result of his foreign policy, and the predominant impression left by a book which is also extremely well illustrated is that a touch of the Lysistrata on Josephine’s part might not have done France, Europe or Napoleon himself any harm.

Philip Thody is Emeritus Professor of French Literature at Leeds University.