Shadowbloods
What he did had made Belialthorn's blood turn cold. When he told Valor what he did, the Ferron did not find anything special or alarming in it.
Belialthorn dipped into his treasure.
Something so forbidden and against his nature to some extent. But then again, losing was very much fully against his nature, so he chose the one he wanted the most.
Belialthorn didn't want to lose here. Not when he already said he would loot the fortress and take their treasure for himself. What he was doing was like borrowing treasure he was to get from the loot in advance.
Belialthorn decided if he was to take down the fortress then he had to start thinking like a Lord. And one thing Lords spend more than anything is the art of war.
This was not the first time that a barrier like this had been used to shield cities from other lord's armies. There were many ways to break it.