It’s hard to make the 12th century—the time of the violent forging of European nationhood, the literary invention of courtly love, and names like Dangerosa and the Lord of Cognac—boring, but biographer/genealogist Weir (The Life of Elizabeth I, 1998) gives it the old Oxford try. Eleanor of Aquitaine was wife to both Louis VII of France and Henry II of England, and her sons with the latter included the legendary Crusader Richard the Lion-Hearted and the King John of Shakespeare’s eponymous play, in which Eleanor also appears as a character. Her unusually long life’she lived to be 82 in an age when women’s average life expectancy was half that’spanned most of the great events of her century. She participated in the ill-fated Second Crusade to Jerusalem (dressed as an Amazon, according to legend), sponsored Provenáal troubadours like Bertrand de Born, and wielded unprecedented political power for a woman of her time (intervening, for example, in the truly Shakespearean power struggles among Henry’s sons after his death). When Weir deals from her professional strength—essentially heraldry, royal genealogies, and Elizabethan misreadings of the earlier period’she is masterful and assured. But in the world of medieval history that makes up the vast bulk of the book, her methodology is inherently flawed. The foreword is one long disclaimer on the difficulties of researching this period, given the scarcity of sources and the stylized, hagiographic tone of chronicles of royal life. Weir is the first to point out the near-nonexistence, in medieval times, of the concept of literary or artistic “portraiture” as we understand it. Despite frequent, almost incantatory repetitions of this truism, she is not above slipping into such psychological solecisms as “The evidence suggests that [King John] was emotionally shallow.” An impeccably researched but pro forma historical biography that comes truly alive only in the vibrantly biased quotations from contemporary sources. (16 pages b&w photos)