Most of the books in the collection date to about 1100. The cathedral’s earliest and most important book is the 8th-century Hereford Gospels; written in Anglo-Saxon characters, it dates to around the year 780. It is one of 229 medieval manuscripts which now occupy two bays of the Chained Library.
The chaining of books was the most widespread and effective security system in European libraries from the Middle Ages to the 18th century. A chain is attached at one end to the front cover of each book, and the other end is slotted onto a rod running along the bottom of each shelf. The system allows a book to be taken from the shelf and read at the desk, but not to be removed from the bookcase.
Here’s a great article about the library: http://www.signature-reads.com/2017/02/welcome-to-the-largest-surviving-chained-library-in-the-world/?cdi=321A47B09DAD4547E0534FD66B0AE227&ref=PRH24BB520913.
The cathedral and its library are open to visitors. Check this website for further information and opening times: https://www.herefordcathedral.org/.