Medivh kept goblins in captivity because he had his eye on their remarkable reproductive rate.
Goblins weren't picky eaters and would eat anything. As long as there was enough food, a few goblins could quickly multiply into a whole tribe.
Gobin young also matured incredibly fast, taking less than a year to reach adulthood.
The goblins kept in captivity at Black Furnace Fortress were harvested at regular intervals.
The harvested corpses were dried and stored.
In just five years, six goblin corpses could be turned into a Grey Bone Skeleton laborer.
With production running assembly-line style, Black Furnace Fortress could regularly produce batches of Low-Grade Grey Bone Skeleton laborers for city construction.
Cheap labor had many benefits. Whether it was farming or odd jobs, large numbers of laborers were needed.
After making a round of patrols with his skeletons, Medivh called Audrey over to unwind. Once he'd rested and recovered his energy, he continued with the smelting and resurrection.
Kurd City had more than enough bones stored in its cellars.
The skeleton legions conducting archaeological work in the wilderness delivered large quantities of bones every day.
The bone trade was booming. The factions in Pioneer Territory were selling buried bones on a large scale, while small and medium-sized factions from beyond its borders traveled to Kurd City in an endless stream, bringing bones to exchange for grain.
Bones accumulated far faster than Medivh could smelt and resurrect them.
There were still plenty of Blue-Grade and Purple-Grade bones in the Underground Warehouse that he hadn't gotten around to smelting and resurrecting.
Medivh was selective when assembling and resurrecting skeletons.
Under normal circumstances, he only assembled and resurrected skeleton types that had already appeared. Complete sets of parts for new skeleton types were kept in reserve.
He saved those new skeleton parts