Crustle have long been known for the enormous, square-shaped rocks they carry on their backs, which they painstakingly carve from caves, mountains, or other large sources of stone and smash against each other when fighting over territory. Whichever Crustle's rock shatters first in these battles is the loser, and that Crustle must retreat, often to the very place they carved their stone in order to rebuild.
For Crustle, the large square shape of their rocks, unusual among rock pokemon, is a way to maximize their effectiveness in this strange combat; rounder rocks not only risk missing outright, but can not be built as large and still be carried by a Crustle, for the square shape distributes the weight of the stone evenly across the pokemon's back. For humans, who pile square rocks on top of each other for functions ranging from fortifications to shelter to monuments to their own greatness, this makes these pokemon the perfect workers.
Humans have at times attempted to enslave the Crustle or steal their rocks outright, but these efforts have met with failure, for humans are far more vulnerable than other Crustle to being smashed by these pokemon's rocks. Those who succeeded in using Crustle for construction did so not only by offering these pokemon ample treats and driving away rivals, but also in transporting them to quarries in covered vehicles, to ensure to the Crustle that they would not be left unprotected on the way back from hauling stones for construction. Crustle, however, are extremely solitary pokemon, dependent on a large territory; despite the best efforts of kings and nobles, these pokemon remain unable to work in teams. However, if the others of their species are driven off, a single Crustle can do the building of a hundred men.
