(NB The following contains minor spoilers for Games of Thrones season 7, episode 1.)

Last week, we were graced with the long-awaited return of everyone’s favorite politically-charged, blood-and-violence-infused fantasy series: Game of Thrones!

While plans of conquest and coalition were being solidified in the season premiere, poor Samwell Tarly was meandering around the Citadel, dealing with the daily drudgeries of his apprenticeship. Sam has to dole out the slop for breakfast, lunch, and dinner, and deal with said slop’s fecal aftermath. But he also gets to hang around books! Chained books, that is.

If you were as confused by that as I was, you’re probably not a medieval history fangirl — and you’re definitely not Oxford scholar B.H. Streeter, who in 1931 wrote an entire book on the phenomenon of chained libraries (aptly titled The Chained Library), quoted last week in a piece about the episode by TIME writer Lily Rothman. Apparently books were so precious in the Middle Ages that they had to be shackled to desks—and, later, shelves—so no one would run off with them forever. Streeter elaborates:

A book, it was said, was worth as much as a farm; unlike a farm, it was portable property that could easily be purloined. Valuables in all ages require protection. Books, therefore, were kept under lock and key. This was done in two ways: they were either shut up in a cupboard (almery or armarium) or a chest, or they were chained, sometimes four or five together, to a desk…

GOT’s nod to history, however, was only a nod: the chains don’t really serve their purpose in the episode, since, y’know, Sam quietly steals a book and doesn’t have to yank any chains out in the process.

Nevertheless, the tradition of chained libraries and the principle illustrated in the episode are one and the same: knowledge is power. In the Middle Ages, illiteracy was a fact of life for most; books were mostly the purview of the ruling class. Information is a valuable commodity in the GoT universe as well — regulated heavily and tucked away from the public in a super-secret-maesters-only vaulted area of the Citadel’s library.

As a symbol, the chained book transcends the border between history and fiction. Robert Rouse, a medieval studies professor at the University of British Columbia, told Rothman, “We can see a lot of that in terms of today, everything from who can access certain websites in China to Wikileaks.” The specifics may change over the centuries, but the general idea is the same. “Information is power,” Rouse reminds us. “And when you hold information you control the narrative.”