Summary

  • In the world of Westeros, several castles are known for their incredible defenses and strategic locations. Here are some of the most impregnable castles in the realm:
  • Harrenhal – This castle was built by Harren the Black, a Targaryen-era king of the Iron Islands, and is considered nearly impregnable
  • Riverrun – This castle is the seat of House Tully and is located near the River Trident. It is known for its strong defenses and has withstood several sieges throughout history



The continent of Westeros in Game of Thrones is filled with renowned castles and fortresses, though some stand out as the strongest and most defensible. The eight seasons of Game of Thrones are based on George R.R. Martin’s A Song of Ice & Fire novel series, but the TV series doesn’t actually make it to each of the well-known castles from the books. Therefore, in order to accurately determine the strongest castles in Westeros, the books and HBO’s prequel series House of the Dragon are necessary for supplementary information and visuals.

Like many elements in Martin’s world, some of the castles and structures in Westeros are built with mystical properties. The fabled hero Brandon the Builder is mentioned in legends as the founder of House Stark’s family tree and is also considered responsible for constructing both Winterfell and the Wall in the Age of Heroes. Regardless of the accuracy of that story, the structures of Westeros include castles of ancient and mysterious origin, with vaguely magical properties that are said to contribute to their defenses.



10 Harrenhal

Harrenhal Is The Largest Castle In Westeros

Harrenhal is the largest castle in the Seven Kingdoms, as proclaimed by Prince Daemon Targaryen in House of the Dragon season 2. Its size and centralized location make it a key strategic point for wars in Westeros, with Tywin Lannister utilizing it in Game of Thrones. Daemon also proclaims in HOTD that it’s necessary to capture for his side, as it’s the only castle with space to amass a large enough army to march on King’s Landing, at least within the vicinity. There are advantages and disadvantages here.

Harrenhal would require forces in the thousands to properly hold.


A castle of Harrenhal’s size is a force to be reckoned with if it can be manned due to its massive, thick walls and tall towers. Tywin Lannister states, “A million men could have marched on these walls, and a million men would’ve been repelled.” However, the caveat with Harrenhal is that, due to its size, it requires a far greater garrison to defend than most other castles. While Ned Stark claims 500 men could defend Winterfell against 10,000, Harrenhal would require forces in the thousands to properly hold.

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9 Pyke

Pyke Is The Island Fortress Of House Greyjoy

Pyke in Game of Thrones


Pyke is a highly unique castle and the seat of power for House Greyjoy of the Iron Islands. It’s built on steep island cliffs surrounded by water, with narrow bridges connecting the multiple keeps. In order to capture the fortress, the attacking side would need a powerful navy to breach the Iron Islands and then a sizable force of knights to take each keep. The Greyjoy Rebellion during King Robert Baratheon’s reign offers stories demonstrating the difficulty, but possibility, of laying siege to Pyke.

As a precursor to Robert’s Siege of Pyke, Stannis Baratheon led the royal fleet along with the Redwyne fleet to defeat Victarion Greyjoy in naval combat. This allowed Robert and Ned Stark’s land forces to reach the Iron Islands, where their siege began. The Siege of Pyke is commonly remembered for the challenge of traversing the bridges, with Thoros of Myr revered for being first through the breach with his flaming sword. Pyke is a tough nut to crack, but it’s not impossible.


8 Riverrun

Riverrun Is The Seat Of House Tully

Riverrun in Game of Thrones

Riverrun is a castle that’s actually been seen in Game of Thrones withstanding a siege. Holding to its name and the reputation of the Riverlands, the best defenses of the seat of House Tully are its water, with moats making it awful to try and storm. Riverrun is between the fork of the rivers Tumblestone and the Red Fork, providing it with access to potential resupply shipments. In A Game of Thrones, Riverrun is described as having its outer walls rise out of the water, with a larger keep situated inside.

Jaime claims that he’s capable of establishing a siege on the castle but that it would take years of waiting for Riverrun to run out of supplies.


In A Feast for Crows and Game of Thrones season 6, Riverrun is besieged by Jaime Lannister and the leftover Lannister forces, hoping to reclaim Westerosi castles as the War of the Five Kings has settled down. Jaime claims that he’s capable of establishing a siege on the castle but that it would take years of waiting for Riverrun to run out of supplies. Instead, he relies on Edmure Tully’s surrender to take the castle. Granted, the Lannister forces aren’t at their full strength, but neither are the Tullys.

7 Greywater Watch

Greywater Watch Is A Moving Castle In The Swamp

Greywater Watch, art by Siddharth and Shruti
Greywater Watch, art by Siddharth and Shruti


Admittedly, Greywater Watch is a bit of a strange pick, as images and descriptions of the castle itself don’t make it seem like the most threatening construction. This is one of the cases where the mysticism of George R.R. Martin’s world comes into play. Greywater Watch is built on a crannog, a man-made structure that allows it to float around in the swampy terrain of the Neck. Not only would an attacking army have to trudge through the marsh to reach it, but the castle itself moves.

Ironborn and Frey attackers have attempted to take the castle but have never succeeded in finding it; instead, they needlessly lose their men to the harsh swamps.

Greywater Watch wouldn’t be the most defensible location if it’s found by its enemies, but there are no records in Westerosi history of that occurring. Ironborn and Frey attackers have attempted to take the castle but have never succeeded in finding it; instead, they needlessly lose their men to the harsh swamps. Greywater Watch hasn’t appeared on either show, but it’s been represented by Jojen and Meera Reed in Game of Thrones. Lord Howland Reed also appears in the Tower of Joy scenes along with young Ned Stark.


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6 Dragonstone

The Island Fortress Of Dragonstone Was Built By The Valyrian Freehold

Like Pyke, Dragonstone benefits from being an island fortress with terrain that would be nearly impossible to land forces on. The only downside of Dragonstone is that its surrounding regions are thinly populated, but it wouldn’t require a very large garrison to defend the castle. Dragonstone is one of the newer fortresses in Westeros, as it was established by the Valyrian Freehold hundreds of years before Aegon’s Conquest and House Targaryen’s history in Westeros.


A plotline that Game of Thrones skips sees Cersei Lannister sending forces to recapture Dragonstone after Stannis leaves it unattended to go north. Loras Tyrell leads the siege of Dragonstone in A Feast for Crows and manages to recapture it with 2,000 men, though the garrison is reportedly minuscule and the defense isn’t well-fought. Dragonstone is also a major strategic location due to its naval potential outside of King’s Landing and Blackwater Bay.

5 Moat Cailin

Moat Cailin’s Environmental Surroundings Make It Impossible To Take

Moat Cailin in Game of Thrones


Greywater Watch isn’t the only castle that benefits from the marsh of the Neck; further north, Moat Cailin is one of the most defensible positions in Westeros. The northern castle was raised by the First Men in ancient times and has effectively been used to defend against southern invasions for multiple millennia. Moat Cailin sits on a natural chokepoint with environmental elements like lizard-lions and deep marsh water contributing to its defenses.

From the south, there’s no record of Moat Cailin ever being captured.

Moat Cailin’s weakness is its north side, which allowed the Kings of Winter to besiege it and bring it into the territory of the North. From the south, there’s no record of Moat Cailin ever being captured. Thousands of years after its construction, the castle isn’t in its best shape, but it’s still a formidable defense that would make taking the North nearly impossible with infantry forces. Catelyn Stark even describes the castle as a “death trap.”


4 The Eyrie

The Eyrie Is The Seat Of House Arryn

The Eyrie looking foggy in Game Of Thrones

Introduced in season 1 of Game of Thrones, the Eyrie is described as “impregnable” by Tyrion Lannister. Like with Harrenhal, the Eyrie is an undoubtedly monstrous structure with incredible tactical benefits in the exemplary scenario, but it’s altogether not the most practical castle in Westeros. The Eyrie would arguably be the most challenging castle in Westeros to storm, as the seat of House Arryn sits in the mountainous Vale region, and the fortress itself sits atop a mountain.

While getting through the Vale is a challenge in and of itself, the Eyrie isn’t as impossible to take as it seems.


However, the flaws of defending the Eyrie are quite apparent, and it can be captured by a sizable force willing to invest the time. If an army can overcome the various mountain gates leading up to the castle, all they would have to do is wait out the defenders. The Eyrie doesn’t have a proper method of resupply, like Storm’s End or Casterly Rock, and it’s uninhabitable in winter due to its elevation. While getting through the Vale is a challenge in and of itself, the Eyrie isn’t as impossible to take as it seems.

3 Winterfell

Winterfell Is The Seat Of House Stark


As Eddard Stark says, “500 men can hold Winterfell against ten thousand.” The feats of the ancient fortress and seat of House Stark definitely support this claim, as it’s a vast castle held by two sturdy walls and multiple towers and keeps within them. Breaching one wall would be an immense challenge, but the second layer of wall is reinforced by a moat, making it even more difficult to siege. If the castle had a sizable garrison, it would be practically impossible to capture by siege.

The defense of Winterfell in
Game of Thrones
season 8 is not representative of the castle’s potential, as they needlessly positioned their forces outside the walls.

Winterfell has some additional clout since it was built by Brandon the Builder. It’s stood for thousands of years and maintains excellent condition. Not to mention, its natural hot springs make it one of the safest locations to be in the North during the winter, and the cold, expansive environment of the North would make it a challenge to reach in the first place. In Game of Thrones, Stannis Baratheon loses a significant portion of his forces before even reaching the walls.


2 Storm’s End

Storm’s End Is The Seat Of House Baratheon

Rhaenyra grieving at Storm's End House of the Dragon season 2 teaser

Storm’s End is one of the mythical castles in Westeros, with walls that have survived the harsh weather of the Stormlands for thousands of years with little wear. It doesn’t appear throughout Game of Thrones, but House of the Dragon offers a glimpse of what the castle looks like. Not only does Storm’s End have a terrain advantage and sturdy walls, but its position above the sea allows for resupply, requiring a simultaneous naval blockade to siege it successfully.


The famous story with Storm’s End is that, during Robert’s Rebellion, Stannis Baratheon held the fortress for nearly a year with only five hundred men against legions of Tyrell forces and the Redwyne navy camped outside, preventing their resupply. Ser Davos earned his nickname, the Onion Knight, by sailing a small boat through the fleet to resupply the defense. Of course, Stannis is a sufficient battle commander, but the story demonstrates the utility of the fortress over a long duration against enormous odds.

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1 Casterly Rock

Casterly Rock Is The Seat Of House Lannister


The seat of House Lannister, Casterly Rock, was shown for the first time in Game of Thrones season 7, and the television version didn’t quite do justice to the impregnable stronghold. Not only are the Lannisters the wealthiest family with one of the largest armies in the Seven Kingdoms, but their ancient castle is also the most durable in the realm. It could be argued for in many ways, but George R.R. Martin himself laid down the law that Casterly Rock is the strongest castle in Westeros on his blog.

On the matter, Martin claims: “The Lannister castle is not ON TOP of the Rock. It is INSIDE the Rock. All of it. Barracks, armories, bedchambers, grand halls, servant’s quarters, dungeons, sept, everything. That’s what makes the Rock the strongest and most impregnable seat in all of Westeros.” The Unsullied used the sewer system to infiltrate the castle walls in Game of Thrones, but under a normal siege, it’s practically impossible that it would ever get captured.


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