Thanks, Donut. Because of your comment I decided to take another look at the Hork-Bajir Chronicles--reminded, once more, why it's probably my favourite book-- and searched for mention of the Council. I then stumbled across this line from Alloran:
<Butchered, Prince Seerow,> Alloran said. <Shall I show you the holos of the aftermath? These were the gentlest pictures. I have others. Would you like to see what they did to the bodies of my warriors?>
I really don't want to imagine what Alloran meant by that.
Edit: And this:
There was talk of creating new ranks. Everyone said that if we were going to become a conquering army, we would need a hierarchy. The ancient Council of Thirteen would remain all-important. But beneath that would come something called "vissers" and "sub-vissers."