Medieval illuminated manuscripts are the holy relics of our own time. They are often preserved, like sacred treasure of the middle ages, in special boxes in institutional strong-rooms and brought out only on special occasions for the edification of the public, displayed in the half-dark under layers of security glass. Unlike most works of art only small portions of any manuscript can be seen at once. What remains unseen merely adds to the mystery and the longing to turn the pages. As with most medieval relics, which are generally tiny fragments of something once much larger, engagement with illuminated manuscripts on public show usually requires great leaps of both imagination and faith.

Despite our centuries-long engagement with some of these manuscripts, there are still surprises to be found. For those of us defined loosely as palaeographers, or historians of early manuscripts, there is always a thrill of anticipation, even after seeing countless great books, when the original of a precious or celebrated illuminated manuscript is placed before you – it is rather like meeting a very famous person. The encounter resembles a conversation or interview. Books talk, with words, and they can answer questions. You have to touch them, not distantly (and preferably not with wretched white gloves), but intimately, peering into the folds and teasing out their secrets from additions and defects as much as from their glorious illuminations and medieval texts. Personally, I want to discover everything. I want to know who made the manuscripts and when and why and where, and what they contain and where their texts came from; why a particular manuscript was thought to be needed, and how they were copied and under what conditions; what materials were used, how long the manuscripts took to make; why and how they were decorated and by whom (if they were decorated, and why not, if they weren’t); and what they cost, how they were bound, who used them and in what way; what changes were made to them later; where they were kept; how they were shelved and catalogued; how they have survived often against all odds; who has owned them, how they were bought and sold and for how much (for they were always valuable), and under what circumstances they reached the custody of their current owners. It is all fascinating. You will make little discoveries almost every time. The trade of being a historian is a licence to impertinence. We can poke our noses into other people’s affairs, and if those people lived 500 years ago, it is called research.

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There are manuscripts once owned by Charlemagne, King Aethelstan, Saint Aethelwold, Otto III, Louis IX, Henry VIII, and countless others, and created for Petrarch, Boccaccio, Gower and Columbus. Turn the pages and you are sharing an actual experience with the great person. To know that a manuscript was commissioned or read by a particular individual will add something to that person’s biography. Books are revealing (as we all know from running our eyes along other people’s shelves), and the connection provides an intimate link, as vivid and evocative as the sight of any relic to a pilgrim.

I have enjoyed deciphering a long-erased inscription in the great Copenhagen Psalter, and realising with a flash of clarity that it belonged to Valdemar the Great, king of Denmark from 1157 to 1182. I believe that I have established the origins of the enormous and mysterious Lambeth Palace Bible, and that it was commissioned by Stephen, king of England from 1135 to 1154, for presentation to Faversham Abbey, which Stephen founded. If the gigantic early eighth-century Codex Amiatinus, the earliest complete Latin Bible in existence, was indeed made in the abbey of Jarrow in Northumbria, then the corrections to its text may be in the handwriting of the Venerable Bede himself. I defy anyone to turn the pages of this incomparable manuscript in its 16th-century library in Florence, designed by Michelangelo no less, without a shiver of excitement. The famous Hengwrt manuscript of The Canterbury Tales, now in the National Library of Wales in Aberystwyth and probably the oldest copy in existence, was made by a scribe – his identity first suggested in the Guardian in July 2004 – who may have been employed by Geoffrey Chaucer himself. If so, this brings us close to the actual presence of the author, which is enormously important for proving the authenticity of this particular version of the text. Every handmade manuscript is slightly different, and textual primacy matters. Peer closely at the volume in Aberystwyth, going back and forth across its pages, and the whole sequence of production falls into place. To anyone able to see and touch the original manuscript, this is almost as intimate an experience as interviewing the author in person, leapfrogging 600 years of history. It becomes a first-hand experience.

It is an odd fact that books, generally speaking, were not esteemed as religious relics in the middle ages, even those that had been owned by canonised saints. Bones and body parts of martyrs were enormously valuable and items of saints’ clothing were preserved and venerated. This shows an interesting difference of attitude between the middle ages and now. If we had a pair of shoes, for instance, that had been worn by William Shakespeare, they would have only minor curiosity value for us, but a book from Shakespeare’s library, if such a thing existed, would be an incomparable treasure today; a window into the intellect and soul of the man.

I remarked on this recently to a fellow historian who said that he knew of an exception. He tapped at his computer and brought up an entry from the sacrists’ roll of Canterbury Cathedral datable to 1321, with a detailed description of a manuscript psalter in a jewelled binding then preserved as a major relic at the shrine of Saint Thomas Becket. I read the entry with one of those moments of heart-stopping recognition that make our careers worthwhile, for I had seen those words before. There is an Anglo-Saxon psalter in the Parker Library in Cambridge with the same description on its flyleaf. It is undoubtedly that actual manuscript. We rushed off together to examine it properly. A 16th-century note claiming that the manuscript had once belonged to Becket has always been ridiculed and dismissed as fantasy, without knowledge of the 14th-century inventory.

Facebook Twitter Pinterest A 13th-century stained glass panel in Canterbury Cathedral depicting Thomas Becket. Photograph: Angelo Hornak/Corbis

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The psalter dates from the very early 11th century, and it was clearly made in Canterbury. Its text shows that it was probably made for private use by an archbishop. A likely candidate would be Alphege (or Ælfheah), archbishop from 1005 to 1012, when he was killed by the Danes in Greenwich. He was canonised as a saint in 1078. Readings commemorating the holy death of Saint Alphege were added into the psalter in the mid-12th century, in the time of Becket. It is likely that the manuscript was found at Canterbury by Thomas Becket, who became archbishop in 1162, and that he then kept it as a personal relic of his martyred predecessor. The almost contemporary stained-glass window on the north side of Trinity chapel in Canterbury above the site of the shrine of Becket shows him holding a book of this size in a similarly decorated binding. Alphege was Becket’s personal patron saint. At the moment of his own martyrdom in Canterbury Cathedral on 29 December 1170, he died commending his soul to Saint Alphege. It is just possible that Becket was holding his psalter. This, then, is a manuscript which was indeed a relic in the middle ages, seen by every pilgrim to the shrine (including Chaucer, no doubt), but which becomes a different kind of relic in our own time, for it is a tangible link with one of the great figures of history. Nothing else imaginable has such personal intimacy.

• Meetings with Remarkable Manuscripts by Christopher de Hamel is published by Allen Lane. To order a copy for £24.60 (RRP £30) go to bookshop.theguardian.com or call 0330 333 6846. Free UK p&p over £10, online orders only. Phone orders min p&p of £1.99.

• This article was amended on 7 October 2016 to correct the year of Alphege’s death.