While Abbess Chiara Vengente lay dying in August 1308, she told the nuns of the Umbrian monastery in Montefalco that Christ was in her heart, sustaining her. When she died the nuns were astonished that after five days her body had still not decayed. Recalling her words, one of the sisters took a razor to the heart and sliced it in half: inside lay a very small image of Christ on the cross, with several tiny objects from the Passion, including the nails hammered into Christ’s body, all “wrought from the flesh of Chiara’s heart itself”.

The art historian Jack Hartnell tells this extraordinary story in his wonderfully rich study of the Middle Ages. Lasting from about 300 to 1500, the period has been characterised since the Enlightenment as an age of darkness, squalor and misery. According to Hartnell this is a calumny. Drawing on exquisite tapestries, illuminated manuscripts, medical textbooks, accounts from doctors and the sick, he reveals the “glittering and diverse” details of medieval life, death and art across Europe and the Middle East.

His idea of approaching the medieval worldview through the body is inspired. The body was at the centre of the physical and metaphysical worlds, an endlessly fecund source of metaphors and ideas around which their imaginative and intellectual lives evolved. Hartnell adopts a literary form from the time, modelled on the human skeleton, which explores the body from “from head to heel”: a capite ad calcem. There are 10 chapters named after body parts. The section on the heart moves from biological theories to a fascinating meditation on ideas of secular love (the ardent troubadours) and then religious love (the cult of the sacred heart): “The medieval heart was a deeply intelligent organ, a unique way of linking person to person, or person to holiness.”

This beautifully illustrated book succeeds brilliantly in bringing this much maligned period to life. Hartnell shows that medieval culture was suffused with bodily tropes, from nuns plucking penises from a tree and flatulists kept by royalty to entertain the court, to the belief that the heart was “a glowing internal sun”. A triumph of scholarship.

• Medieval Bodies: Life, Death and Art in the Middle Ages is published by Profile. To order a copy for £21.25 (RRP £25) go to guardianbookshop.com or call 0330 333 6846. Free UK p&p over £10, online orders only. Phone orders min p&p of £1.99.