From Introduction:
When the empire of Mëolgysst ruled over these lands, its kings and sorcerers built safehouses to store the treasures they looted from their neighbours. These were more common in times of war and conquest, for when peace would settle, loot was displayed in the palaces of the capital. But even then, this morbid nation’s rulers would often grow jealous and paranoid, preferring to stash their ill-gotten gains in lands obscure. And of course, these repositories needed guardians.
The crystalline carapace constructs were common in Mëolgysst for several decades, then they became rare, and finally the art of their construction was lost—mercifully so, perhaps, for they were, and still are in some cases, powered by the flesh of those buried alive inside them. Hollow statues of hard crystal were filled with freshly-slain bodies, to be animated by the necromantic residues of their ghosts. The flail knight, with his trusty ratdog, was a common motif.
Some of these storehouses have been buried by time or natural
disasters, their guardians still waiting for intruders to bring them to life. Others have been looted, their treasures gone and their guardians destroyed. But some of these guardians have been expropriated by wizards who repurpose them for their own benefits. They are not exactly common, but they have been employed more than once in famous circumstances.