All castles in Heroes 3.

Definitely within a month! And the Citadel has Cyclops that require 20 stone and 20 crystals, which is almost like dragons – 30 stone and 20 crystals. Monsters require 10 crystals, and the same Pegasi require 10 crystals. Dendroids only need gold. But the Citadel really needs a lot of stone and wood; in total, the Rampart needs even less, but it requires 2 magic towers.
So, celt was right.