There are only four books in the main series, and none of them are too terribly long. But if you’re a completist, there’s no limit to how deep you can dive into what the author called his "legendarium.

The War of the Rohirrim takes place about 250 years before the events of The Lord of the Rings, during the reign of Helm Hammerhand, king of Rohan. Or, to give you another kind of perspective on things: Helm’s Deep, the massive mountain fortress where the climax of Peter Jackson’s The Two Towers takes place? That’s named after Helm.

The War of the Rohirrim anime debuted in theaters on December 13, but you can already preorder the limited-edition 4K Blu-ray release for $38 at Amazon.