The tribe leaders who learned about Coelus's corpse from their elders were silent throughout Aillos's narration of the recent events. They had an inkling that Aillos would reveal the truth about Coelus's tomb underground if he intended to wage a war. After all, if the battlefield happened in their plane, and The Emperor went all out, their plane's topography would be drastically changed. When that happened, the seal on Coelus's tomb would be destroyed, and the dragons would suffer from the influence of his corpse's magic energy. The consequences of such a war were too grave to contemplate.
To avoid that, Aillos had to come clean about the tomb and ask for everyone's cooperation to ensure the war would not come to their plane. Another option they could do was transfer Coelus's corpse to another place, but the problem was replicating the seal that the Ancients created.
