Tresoar houses the so-called Richthofenkolleksje, the collection of books by Karl Freiherr von Richthofen (Damsdorf, 1811 -1888). Von Richthofen studied the history of law in Berlin and Göttingen, and became fascinated by Frisian legal history. He collected and studied sources until the end of his life in 1888. Tresoar preserves the collection that was created partly through his efforts and fascination. It comprises 10 manuscripts focusing on Frisian land law and Frisian history, often also written in Frisian. The oldest manuscripts date from the mid-14th century, the youngest from around 1600. It is a rich treasure trove of information on medieval Friesland, regional law and also the history of Frisian as a language.  That is why it has been included in the Unesco Memory of the World Register: https://www.unesco.nl/nl/nl-memory-world-register/richthofenkolleksje

A full website about the Richthofenkolleksje (in Frisian and Dutch) can be found at this site: https://richthofen.nl/