‘Hairy” medieval book covers previously thought to be made from deer or boar skin are in fact made of sealskin, researchers have found.

The covers of the 12th- and 13th-century books from French monasteries were made using seals believed to be from Scandinavia, Scotland and potentially Iceland or Greenland, hinting at extensive medieval trade networks.

Researchers analysed volumes from a Cistercian monastery, Clairvaux Abbey, and its daughter monasteries, identifying 43 sealskin books.

“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,” reads the research article, published today in Royal Society Open Science.