At the Battle of the Blackwater a massive chain had been raised between two winch towers at the mouth of the river. It was mentioned in Chapter 15 of A Clash of Kings that a thousand links were constructed for it.

Now I don't know how big the links were exactly or how wide the river is, but it seems to me that raising such a huge chain requires an extremely large amount of force, and to keep it raised when ships crash into it requires even more force; so it seems to me very unlikely that it is possible.

So I wonder: how would such a chain even work (in-universe)?

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    en.wikipedia.org/wiki/Hudson_River_Chain probably
    – Himarm
    Mar 14, 2016 at 21:36
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    @Himarm, interesting, I didn't know those kind of chains were used in real life, I thought it was made up for this story. All those links are interesting to read. The information in there would make a great answer.
    – Ivo
    Mar 14, 2016 at 21:41
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    How does the chain used at the Battle of the Blackwater work? All together now... very well, thank you. Mar 15, 2016 at 17:42
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    A similar chain was used in real life in defense of Constantinople from Turkish forces
    – Timpanus
    Mar 15, 2016 at 19:07

1 Answer 1


As a pre-cursor to this answer, as pointed out in the comments by @Himarm, Harbour Chains were in fact used as navigational barriers (and are still used to this day), so it's not actually a stretch for the chain to have done what it did.

The chain was humongous, strong and taut. It easily reached all the way across the bay. It was built by ALL of King's Landing's smiths and metalworkers:

... The gaggle of smiths, armorers, and ironmongers that Bronn had collected fell to their knees.
He hoisted himself up into the high seat under the round golden window and bid them rise. “Goodmen, I know you are all busy, so I will be succinct. Pod, if you please.” The boy handed him a canvas sack. Tyrion yanked the drawstring and upended the bag. Its contents spilled onto the rug with a muffled thunk of metal on wool. “I had these made at the castle forge. I want a thousand more just like them.”
One of the smiths knelt to inspect the object: three immense steel links, twisted together. “A mighty chain.”
“Mighty, but short,” the dwarf replied. “Somewhat like me. I fancy one a good deal longer.
“I want every forge in King’s Landing turned to making these links and joining them. All other work is to be put aside. I want every man who knows the art of working metal set to this task, be he master, journeyman, or apprentice. When I ride up the Street of Steel, I want to hear hammers ringing, night or day.
-A Song of Ice and Fire: Book Two - A Clash of Kings, Chapter Fifteen (Tyrion III).

It was fastened on both ends to watch towers and raised using a lever and pulley system:

He [Davos] saw no sign of any boom; the mouth of the river was open, as if to swallow them all. Except
The squat towers of raw new stone that stood opposite one another at the mouth of the Blackwater might mean nothing to Ser Imry Florent, but to him it was as if two extra fingers had sprouted from his knuckles. Shading his eyes against the westering sun, he peered at those towers more closely. They were too small to hold much of a garrison. The one on the north bank was built against the bluff with the Red Keep frowning above; its counterpart on the south shore had its footing in the water. They dug a cut through the bank, he knew at once.
Something flashed down low where the dark water swirled around the base of the tower. It was sunlight on steel, and it told Davos Seaworth all he needed to know. A chain boom... and yet they have not closed the river against us. Why?
-A Song of Ice and Fire: Book Two - A Clash of Kings, Chapter Fifty-Eight (Davos III).

Further reading:

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    I know the OP asked for in-universe answers, but here's a link to a Wikipedia page regarding real world chain booms. Might help... en.wikipedia.org/wiki/Boom_(navigational_barrier)
    – nedlud
    Apr 13, 2016 at 3:43
  • Thank you @nedlud. I've used that exact link in the answer :)
    – Möoz
    Apr 13, 2016 at 5:56

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