Control Spire

Digimon Adventure 02
The Control Spires were created by Ken Ichijouji, under the influence of a Dark Spore making him the Digimon Emperor, and prevented natural Digivolution. The only form of digivolving that the Control Spires could not prevent was Armor Digivolution. This was available when the Sovereigns turned the Crests, which had been used to save them after the Dark Masters' rule, into Digi-Eggs, which gave the new Digidestined the power to defeat Ken and restore him to normal.

A while after, Arukenimon and Mummymon began turning these Control Spires into Digimon. They brought together 100 Spires to create BlackWarGreymon. Unfortunately, he felt they were inferior to him and went to find himself. Soon, several spires found their way into the Real World, as well as some Digimon that began terrorizing humans around the world.