The Seven I can''t think of the word. It''s not ''distant'' or ''obscure'', these are too cold. But it''s not ''exotic'' either. What''s the word for this, the thing that horrifies you but then unlocks your heart? In my hands is a book written on lambskin seven hundred years ago. It''s tall, like an oversized restaurant menu. The pages are yellow, the spine has the waxy feel of dead skin, and it smells of damp gardening gloves. It weighs roughly the same as a large fresh salmon. I''m sitting with it in the Vatican Library, and under the flash of the archivist''s spectacles I feel like the skinned lamb myself.

Usually this book is kept in a concrete vault. You have to show your credentials at the front gate and surrender your passport to the Swiss Guards. Next you have to go through a brief interview, get your photo taken, sign several forms, and leave all your things in a digitally activated locker. Only then, after you''ve stripped off your modern identity, are you allowed to climb the stairs and get your hands on this, the world''s only copy of the Ark of Wisdom.1 Is it worth travelling to the Vatican City for? Opening up the 650- year-old manuscript, I find every combination of anxiety and desire. And although the ink is ancient, the ideas are as fresh as if they had been written this morning. Across the 300 pages there are ecstasies and passions, rages and fantasies, procrastinations and jealousies. So many of the thoughts I imagined were mine alone- thoughts exhilarating, petty, lonely or afraid - are here, exposed in brown Gothic handwriting.

There are the telltale signs of hypocrisy; the ''right'' and ''wrong'' kinds of personal grooming; the best remedies for depression.2 The book pulses with energy, as if every word were written by somebody who already knew our world was coming. I shouldn''t be surprised that this manuscript feels so alive. It was structured around a sixteen-hundred-year-old system that still works; a map that continues to function as a reliable guide to the human brain. Because the Ark of Wisdom is really a handbook for how to live with the Seven Deadly Sins. For most of us in the twenty-first-century the Seven Deadly Sins are a bit of a joke. Not too long ago they inspired a range of ice creams, with a pink strawberry ''Lust'' and a peanut-butter ''Sloth''. Graphic novels have made them into villains, and video games have made them into end-of-level bosses.

It''s still possible to stream Se7en (1995), the blockbuster movie starring Morgan Freeman and Brad Pitt, which features a serial killer who punishes people for each sin in turn (although in the wrong order). But in the Middle Ages the Deadly Sins were more than a gimmick. They were psychological tools, keys for deciphering personality and decoding desire. They were a Periodic Table for the mind. As desert monks like John Cassian described them, the sins were a system for ordering and processing all thoughts. Every tempting idea and harmful act, in theory, could be traced back to some combination of these seven.3 What are their names? And what''s their ''correct'' order?4 Listing them in their classic form - and in their usual ranking, from most to least ''deadly'' - the seven are: 1. Pride : Self- obsession, to the point of dismissing the lives of others.

This usually grows out of your focus on yourself. 2. Envy : Craving for other people to fail, or for their successes to be crushed. This usually grows out of your focus on others. 3. Anger : Frenzy, rage and a loss of the power of reason. This usually grows out of your impatience with others, or with yourself. 4.

Sloth : Despair, depression, or falling out of love with life. This usually grows out of a lack of focus. 5. Avarice : Questing for more and better possessions. This can also cover ''wasteful'' generosity, or fixation on different objects. It usually grows out of a focus on material things. 6. Gluttony : Excessive desire for food, alcohol, or other consumables.

This can also cover total abstinence from eating, or excessive connoisseurship. It usually grows out of a focus on necessity. 7. Lust : Fixation on sex, but also sensory pleasure. It usually grows out of a focus on bodies. The Ark of Wisdom moves through each of these seven with the precision of a sniper and the compassion of a kidney donor. Written sometime in the late 1300s, it has rarely been cited or copied since. In fact, it remained more or less unknown beyond the monastery near Milan where it was first kept.

So, reading it now, in the Vatican Library, is a moving experience. But really, the Ark of Wisdom is only the beginning. Out there in Europe''s archives are thousands of works just like this one: books that use the Seven Deadly Sins to explore temptation, frustration, fear, anxiety, grief and passion; guides for coping with rage and narcissism, and for embracing life''s positives. Obstacles keep these books out of our reach. Most are inaccessible, written in obscure languages and torturous handwriting. Also, they''re usually packaged under two labels - ''medieval'' and ''theology'' - that don''t always excite the average reader. And this is an enormous loss. Because if these guides have a true home, it isn''t in the concrete vaults of a library building.

And it''s not in a university research seminar, either. It''s in the hands of all of us, as we struggle through these labyrinths we get thrown into. The dark mazes of our lives. A Pink Sky A few years ago I fell into a trap that nearly swallowed me whole. It was a trench packed with unforgiving snow, and it was one I had dug all by myself. I was teaching medieval history at a university in Siberia. Winter was approaching, and it was already bitterly cold. Below around minus 20ºC my eyelashes grew tiny icicles.

Beyond minus 25ºC, if I stayed outside for longer than twenty minutes I could no longer feel my legs. I spent my afternoons in shopping malls, browsing leather bags and microfibre hats. I ate herring salads in cafés with pictures of the Eiffel Tower on the walls. Snow covered the pathways like fresh earth on a casket. Soon I found I no longer thought about the future. I stopped reading the news and I stopped contacting my friends. Then I stopped going outside at all. In my apartment I just stood by the window, pressed up against a radiator, watching as chimney stacks puffed smoke into a pink sky.

History can be an escape portal. It can transport you to a different life, a different heart. This was a lesson I began to learn when I was nine. One afternoon, early in the school holidays, my mother took me on the Piccadilly Line to the National Portrait Gallery in London. I stood in front of a picture of Richard III, the king who had been his mother''s twelfth child and who had died at the Battle of Bosworth Field in 1485. I looked at the faded lines of his black robe, his crooked fingers with their colourful rings, and his luminous, desperate face, and I felt something inside me spike. Part of it was horror. To live in a world so different.

To be bludgeoned to death in a muddy field with a halberd axe. For this to be a plausible life outcome. But alongside this horror was another feeling. I found I was burning to lift the veil, to cross the abyss. I wanted to discover what life was really like for the people on the other side of this window of oil and wood. Over the next three decades I chased that mystery I''d seen in the Middle Ages wherever it led me. It was a quest that took me around the world. For a while I lived in the basement of a second-hand bookshop, absorbing shelves of books with foxed endpapers and titles like Cistercian Monasticism.

At university I became obsessed with medieval mystics, and wrote a musical comedy about the twelfth-century lovers Abelard and Heloïse. Moving to New York to do a PhD, I found my mentor, a French scholar who taught me to look for clues to medieval psychology in obscure Latin texts. I travelled between the archives of Paris and London, and I hunted through the margins of forgotten manuscripts. I published articles in academic journals, gave papers at conferences and found teaching jobs, first in Toronto and then in London, just a few hundred yards from the National Portrait Gallery. On quiet days I sometimes went back to visit King Richard, to thank him for all the glamour he had brought me. And then, for reasons that are still opaque to me, I moved to the city of Tyumen in Siberia. Some of my motivations were fairly rational, in hindsight. My contract in London was ending and the job advert was enticing.

The challenge of the climate and language appealed to me, and I was curious to see what medieval Europe might look like to people who had grown up under Vladimir Putin. When I sat explaining these reasons to my friends, it did occur to me that they didn''t amount to much, but I left these doubts behind when I arrived in my new home. At first I loved it. My days were filled with walks through silver birch forests. The snowflakes shone for me in the heavy air like diamonds. On the wall of my new apartment the landlord had hung a framed photograph of the cosmonaut Yuri Gagarin waving to a cheering crowd on a Moscow street. And most days I waved back. But over time I stopped waving at Yuri.

Over time the coldness in my life stretched beyond the hard fact of the weather. After days of heavy teaching, I would wake up with an ache that flowed from the stem of my brain into every capillary of my bloodstream. I was supposed to be researching and planning my lessons, to be getting on with my life. But I couldn''t bring myself to do anything at all. Standing by the window, my spirit disappearing with the smoke in the sky, I realised I had nothing to.