So the dreadnaught is roughly the size of the moon, and it's made from the husk of a worm God Akka. Oryx killed Akka one of 5 worm gods. If one worm God is the size of our moon how big is the fundament? [spoiler]the fundament is a giant gas "planet?" That held the hive on its surface and the 5 worm gods at its core. [/spoiler]
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I could be wrong, but I thought the dreadnought was made from a bone of the leviathan from fundament. Oryx killed the worm god to get the tablets of ruin, but used the leviathan carcass for his ship.