Siege Crabs are amphibious war machines invented in the Horgon Era by the kuo-toa city-state Fongruk-Toa. They are made from titanic crustaceans that suffer arcane infusion which is both debilitating and terribly painful. All the time this is happening, a dozen or more priests are applying their healing arts on the hapless creature. This process, though refined over the epochs, still only results in 60% of the creatures surviving. In some cases, the creature breaks free of the arcane leashes holding it in place. Such is the strength and destructive force of these creatures, that they wreck havoc on everything around it. In the early stages of Fongruk-Toa, one of them breaking free would often result in the ruin of an entire town or even the city around it. As the empire grew economically, they constructed massive pens for these beasts and in them performed the ceremony of combining the arts of wizards and priests to turn a colossal-sized crustacean or greater into a willing servant and war machine.
In the First Epoch, Tinnanguth spies stole the know-how of making siege crabs from Fongruk-Toa. Until that empire fell, these siege crabs made them the mightiest sea power of the Pearl Sea.
Late in the Third Epoch, Ora Tubruš began constructing siege crabs. They came upon this ancient technology from the adventuring group Zhuts Cutthroats. In 1834, this group plundered long lost tomes of siege crab making from the Tinnanguth ruin Liope. The ruins of the Tinnanguth empire are littered with the wrecks of siege crabs for even though they are long dead, their bodies have suffered nothing from time and the elements.