A hero who hedged his bets

Blenheim Palace, Sir Winston, Princess Diana... the legacy of John and Sarah Churchill, Duke and Duchess of Marlborough, continues to make its mark on a nation that was enthralled by them in the early 18th century. In worldly terms, the Marlboroughs could hardly have been a more successful couple; they rose from the ranks of the middling gentry, met at court, married and made themselves indispensable to four successive monarchs, accumulating property, titles, positions and truly staggering quantities of cash on the way. Marlborough's military successes in the drawn-out Wars of the Spanish Succession were not just strategically important, but bolstered up the nation's self-esteem and identity in troubled times. He was a reliable, home-grown hero, on hand to save king and country - however Catholic or foreign those might be.

But the Duke was also a genuinely problematic figure, whom his new biographer Christopher Hibbert has no intention of passing judgment on. His career was not always smooth nor his behaviour defensible. Described by one contemporary as "a profound dissembler", Marlborough dodged from side to side during the reigns of James II and William III. And though he certainly kept his head down during James II's most flagrantly Catholic outbursts, his toleration of them and the King's earlier persecution of the Scots Covenanters hardly count as "never acting against his Protestant consciousness", as Hibbert claims. Marlborough's Protestant consciousness only really stood up to be counted when it saw William of Orange land; he deserted to the invaders on the way to fighting them.

The Orange regime turned out to be one in which Dutchmen got promotion much faster than old demi-Jacobites, and Marlborough kept his bets carefully hedged all through the 1690s, maintaining contact with the exiled James. And during the resurgence of the Stuart claim in 1715, he ingratiated himself with the Pretender, just in case.

Less "unfathomable" - because she was such a loudmouth - was the career path of his wife Sarah. Sharp, beautiful and self-dramatising, Sarah endeared herself to Princess Anne while the latter was still a teenager and became the unassailable power behind the throne when drippy Anne acceded. Anne was such a soft touch, loading the Marlboroughs with sinecures and insisting on lavish gifts from the public purse, that it's no wonder Sarah became irrationally demanding and headstrong in response, eventually provoking dismissal because of her harangues and spiteful fights with the monarch. Anne, unhealthily fat and old before her time, comforted herself with a new favourite, Abigail Masham, and took to driving very fast in a carriage.

A lovers' tiff ? Christopher Hibbert isn't going to be drawn on this, or on much else that lies outside the line of data. He doesn't seem to have anything new to contribute to controversial episodes in Marlborough's life such as the "Flowerpot Plot" of 1692, the question of whether Marlborough embezzled army money or the supposed affair with Hester Santlow (which Hibbert assumes was "phantom" and his wife's fury groundless). With so many military battles to describe in detail (which he does very thoroughly) perhaps Hibbert felt that there was no room in his book for speculation. Unfortunately, history-writing seems not only duller but less trustworthy when few questions are asked.

We are left with the material facts of this materialistic couple's lives; the wife's financial flair (she made a killing out of selling South Sea stock just before the Bubble burst), the husband's parsimony (he would rather walk home than spend sixpence). Being exceptionally rich and exceptionally careful, they of course quarrelled with everyone, including their own children, and plodded on with the building of monstrous Blenheim Palace - mostly paid for by a grateful nation - though the Duchess certainly never wanted to live there and the Duke died before it was finished. It remains a remarkably appropriate monument to their ambitions.