A new study of 12th and 13th century manuscripts from the Library of Clairvaux Abbey in France has found 43 of them were bound in sealskin imported from the north Atlantic, not from locally sourced animals like deer or boar as previously believed.

The Cistercian monastery of Clairvaux Abbey has a collection of manuscripts that has been prodigious since the Middle Ages. It already had 1,000 volumes in the library by the early 1500s, most of them copied in Clairvaux’s own scriptorium, and today there are 1,450 medieval books in the collection. About 50% of them are in their original bindings, which is extremely rare for medieval manuscripts as they were often rebound. Of the 168 surviving original bindings from the 12th to the 14th century, 28 are still intact, and because the majority of them were produced in-house at Clairvaux Abbey, they are a uniquely rich source of information about how workshops manufactured books in the Middle Ages.

The Romanesque manuscripts copied and bound in the Clairvaux scriptorium have a distinguishing characteristic: a secondary cover known as a chemise made of leather that retains animal hairs. Historical catalogues describe these skins of being made from deer or boar, but their hair follicle distribution on the skins does not match either deer or boar.

To determine which animals’ skins were really used to create the chemises, researchers deployed microscopy, electrostatic zooarchaeology by mass spectrometry (eZooMS) and ancient DNA (aDNA) analysis on 29 bindings from Clairvaux and its daughter house Clairmarais. The eZooMS analysis classified seven of bindings as having been made from seal leather, although it could only narrow down the species of seal in one case (it was a bearded seal). The aDNA analysis was able to go further, identifying four of the bindings as harbor seal leather and one as harp seal from the northwest Atlantic, namely Scandinavia, Scotland and Iceland or Greenland.

Armed with this surprisingly revelation, researchers looked for manuscripts with hairy chemises in other collections. They analyzed another 13 bindings from abbeys in France, England and Belgium and discovered that they too were made of sealskin. There is no mention of sealskin in the Clairvaux Abbey records, nothing about their acquisition or their use, but there are records from the late 13th century that document tithes being paid to the Church with seal skins. Clairvaux and its daughter abbeys were also located near local trading routes linked to the wider network of the Hanseatic League and to Nordic traders, so they had access to pinniped skins even if they weren’t tithes. They might not even have known they were seal skins, as seals were not seen much in medieval art and heraldry.

Contrary to the prevailing assumption that books were crafted from locally sourced materials, it appears that the Cistercians were deeply embedded in a global trading network, acquiring skins through extensive trade exchanges. This observation extends beyond just the bindings to include most of the materials used for both the covers and the parchment of the text blocks. While librarians, palaeographers and codicologists have struggled to identify the origins and provenance of these skins solely through conventional literary sources, the disciplines of biology and biocodicology offer invaluable insight. The integrated approach used in this study not only enriches our knowledge of Cistercian manuscript production but also highlights the broader economic and cultural exchanges of the medieval period.

The study has been published in the journal Royal Society Open Science and can be read here.