An absorbing travel book, a meditation on geology, photography, Romanesque art and the romance of physical decline, The Slow Breath of Stone throws a mirror on Europe of the Middle Ages and its hold on us today.

In the years following the devastations of the first world war, a brilliant, young American couple, Kingsley and Lucy Porter, travelled to south-west France to document the abbeys and basilicas of the Romanesque period. Their extraordinary photographs revealed some of the most feverishly inventive stonescapes in Europe, stories chiselled from the Bible and nightmares: rams playing harps and devils eating men's brains; a female centaur pulling a mermaid's hair; women suckling snakes at their breasts. For the Porters, these were images of an imagined world that unlocked secrets of the eleventh century but, menacingly, cast a dark shadow over their marriage.

In The Slow Breath of Stone, Pamela Petro rents a car and, using the Porter's photographs and Lucy's journal as her map, retraces their journey through the wild landscapes of the Rouergue. She visits the beautiful and disturbing sculptures of monsters and animals devouring prey that adorn the cathedrals of Cahors and Carcassonne, and she explores a limestone quarry from where these great slabs of stone were hewn a thousand years ago. She walks the routes of pilgrimages, testaments to the tenacity of human hope, meeting people along the way and savouring the local food and wine. Above all, she journeys deep into the strange relationship of the sexually incompatible Lucy and Kingsley, following them to Donegal where their marriage was to end tragically and mysteriously on the cliffs of Inishbofin.