Hildegard of Bingen, 12th-century prophet extraordinaire, would not have been alarmed by the outbreak of Y2K fever, but she would have known how to seize the moment. Eight hundred years ago, readers treasured yet trembled at her predictions of the apocalypse to come, asking: When will the ominous ‘Age of the Fiery Dog’ begin? Which monasteries were to be seized by secular lords, humbled and disendowed? Had the Antichrist already been conceived in his mother’s womb? Was there still time to avert the threatened wrath of God?

In later centuries, Hildegard would be credited with predicting everything from the English Reformation to the Napoleonic Wars. Protestant polemicists saw her as a reformer avant la lettre, while other parts of her legacy were claimed by Catholic humanists and esoteric philosophers. After a long eclipse, her star rose once more in the 1980s, and for the last twenty years she has been the darling of early music lovers, Christian feminists, holistic health practitioners and New Age spiritual seekers. During her 900th birthday festivities in 1998, pilgrims flocked by the busload to the Rhineland abbey she founded, the home today of a flourishing Benedictine community. By the time the nuns of Eibingen had received 150,000 guests in six months, they decided that it was time to pull down their cowshed and build a visitors’ centre. At the Vatican, however, Pope John Paul II disregarded a petition to complete Hildegard’s formal canonisation process (aborted in 1243) and declare her a doctor of the Church. Evidently, this most uppity of medieval women is not a model the Pope wants to raise up for emulation in the new millennium.

The popular cult has been accompanied by a scholarly boom: at least four essay collections devoted to the visionary abbess appeared in her anniversary year. At the same time, capable translators have begun to make Hildegard’s voluminous writings available to non-specialists. Yet admirers excited by her unconventional life – her visions, her forays into medicine and music, her bold denunciations of bishops and emperors, her celebrity as a preacher – may be nonplussed by a first exposure to her writings. For Hildegard was at once prodigiously learned and, as she somewhat disingenuously claimed, ‘a poor, uneducated little female’. The point of this claim was to underline the prophetic authority on which her career depended: since she lacked human instruction, her mysterious wisdom could have come only from God, who ‘chose what is foolish in the world to shame the wise’, as St Paul had written.

But there is also some worldly truth in the claim, for Hildegard was one of history’s great autodidacts. Borrowing books from the libraries of her monastic friends, she read everything she could lay hands on, from standard Bible commentaries to obscure astronomical treatises and the latest translations of Arabic medical writers. Yet she lacked what every Benedictine monk began to acquire at the age of seven: a solid grounding in Latin grammar. To the end of her days, she needed a copy-editor to correct her cases and tenses; she never mastered the subjunctive; and her rhetoric owed more to the Hebrew prophets than it did to the polished, humanistic Latin of her contemporaries. The combination of Hildegard’s rough-hewn style with her daunting range is what makes her so difficult – not to mention the veils of allegory that she and other prophets deliberately used to cloak their sensitive political message. Hildegard may be best appreciated in small doses, although she wrote mainly in large ones. Even in the Middle Ages, her public knew of her visions through anthologised snippets; her original books were too long to be frequently copied, let alone read.