‘Game of Thrones’ 101: What You Need To Know About Casterly Rock

The ancestral home of House Lannister is getting some serious attention in Season 7 as war brews in Westeros

game of thrones casterly rock map

(Spoiler alert: Please don’t read on if you haven’t watched Sunday’s episode of “Game of Thrones”)

Although it’s incredibly important to the politics of “Game of Thrones,” there’s a major location we have yet to see in the HBO show: Casterly Rock.

The seat of House Lannister, Casterly Rock was referred to by Tyrion Lannister (Peter Dinklage) as the true seat of power in Westeros. The Lannister homestead is the site of Lannister wealth, and House Lannister has been lending all kinds of money to King’s Landing for years. With Cersei crowned queen in Season 6, Lannisters effectively control the continent, even if they have trouble consolidating their power.

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In Season 7, Tyrion laid out a plan to send Daenerys’ forces to attack Casterly Rock and capture it from the Lannisters, cutting off a key component of their empire. But what makes Casterly Rock important, and more importantly, where is it?

Casterly Rock is located on the western shore of Westeros, due west and a little north of Dragonstone. The castle is literally built on a big rock that overlooks the Sunset Sea. The castle is, also literally, a gold mine — one of the best-producing mines in the country, in fact. That gold mine is where the Lannisters get all their money from.

But there’s a key caveat about the wealth of Casterly Rock: It’s gone. The gold mine was depleted years ago, and the Lannisters have been lending money to the Iron Throne for years while Robert Baratheon was king. The crown was in major debt to the Lannister family. So while the Lannisters are known for their wealth, they don’t actually have any at this point.

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Legend has it that Casterly Rock was previously held by House Casterly thousands of years ago, long before the conquering of the Seven Kingdoms by the Targaryen dynasty. Lann the Clever, one of the legendary figures during the Age of Heroes thousands of years ago, managed to swindle House Casterly into giving him the house, so the stories go. Accounts vary on how exactly he did that, but he’s the guy House Lannister claims to descend from.

Like Winterfell in the North, Casterly Rock is the location from which the Warden of the West governs the entire region. That warden was Lord Tywin Lannister until he was killed. (There are two other wardens: the Warden of the East has traditionally been the leader of House Arryn, Lord Promentory and Defender of the Vale, and the Warden of the South has traditionally been the leader of House Tyrell in Highgarden.)

The location of Casterly Rock on the western coast of Westeros is important in Season 7. Part of the war plan Tyrion laid out in Episode 2, “Stormborn,” was to capture Casterly Rock from Cersei to undercut her power in King’s Landing. The plan is to send the Unsullied to attack the Rock and capture it — but the distance between Casterly Rock and Daenerys’ base on Dragonstone on the eastern coast of Westeros is significant, the width of the entire continent. (Here’s what you need to know about Dragonstone.)

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The plan Tyrion explains has the Unsullied sailing for Casterly Rock to attack it, rather than marching over land, which would take them all the way around the southern end of Westeros. That long trip is presumably safer and maybe even be quicker than an overland march, but Casterly Rock is still pretty far way, and it’ll probably take days or weeks for the Unsullied to arrive.

Tyrion also has some special knowledge of the Rock. He explains in Season 7 Episode 3, “The Queen’s Justice,” how his father Tywin rebuilt the Rock, and made Tyrion in charge of the sewers. That’s how Tyrion knows about a secret tunnel that Grey Worm uses to infiltrate the fortress and capture it.

But with no gold in Casterly Rock, it’s not the jewel that Tyrion seems to think. In fact, Jaime leaves the fortress mostly unguarded, and instead takes the Lannister army elsewhere. When Grey Worm captures it, it’s a hollow and costly victory.

“Game of Thrones” airs Sundays at 9 p.m. on HBO.