User blog comment:Observer Supreme/Who built the Tower of Heaven?/@comment-26523876-20160125001721

The Tower of Heaven was built by all those slaves they had kidnapped. Erza, Jellal, Simon, Millanna and many other children and or adults were kidnapped to help build the Tower of Heaven to resurrect Zeref using the R-System. The cultists were the ones who kidnapped the children. The Magic Council used the Etherion Cannon thinking it would destroy the tower but instead it turned the regular Tower of Heaven into a tower that was made of Ethernano(or whatever the correct term for that stuff is if I didn't get it right). Ultear was involved because SHE(not Zeref)possessed Jellal and forced him start back building the Tower of Heaven. Grimore Heart did want Zeref but they weren't responsible for the Tower of Heaven incident. It just so happened that Ultear joined the Grimore Heart guild.