The ancient mage-emperors obviously did not know how to effectively suppress the First Born, because they were all defeated. The First Born was forced to fall asleep under the influence of the safety device, and they had not really found a way to kill this primal creature. Therefore, after the First Born fell asleep, the suppressive measures they took were basically a gamble: each mage-emperor chose a different form of sealing in the hopes that they would work.
The mountainous barriers of Dragonspine Ridge and the lifeless rock monsters were proven to be ineffective, while the Giant Tree of Life was said to have withered. Now, the only seemingly functional and powerful seal was the Volcano of Dusk.
