Bloodlantern Chain

"The thing the Sable Tower doesn't want you to know is that for centuries, Karthani society's rotted from within. There's only so much you can do with a society like that. Oh, sure, they have magic, don't get me wrong. They're dangerous and scary, but you go around kidnapping, selling your services to the highest bidder, trying to control every aspect from behind the black stone of the tower, and you're cutting off your own feet. People get angry when they see their young getting kidnapped, and when people are angry, things clash. The Sable Tower's not as all-knowing as they want you to think they are. They're mortal, and every mortal's got their blind spots, even the black bastards." The one-eyed man scratched at his chin, then, and took a long drink from his mug. There were few people around to hear what would, in Karthain, get him spirited away. They were beyond the borders of that land now, and the boy he'd rescued from the magi escort said nothing in response. The boy would not be captured again, and he would make the Sable Tower pay for what it did to his family.

— Ilbasmis Pamuk -- Memoirs of a Magus

The Bloodlantern Chain is an underground society opposed to slavery and the totalitarian control of the Sable Tower. They seek to undermine the Tower's power by frustrating their efforts to locate and acquire magic users, aiding in the escape of captured magic users and slaves, and assisting in the research and creation of anti-magic devices. The Bloodlantern Chain existed when Karthain was still Rumain territory, though it existed then purely as an anti-slavery organisation. Some Bloodlanterns are not as opposed to the Tower and the magocracy as others; the most common reason people join is an opposition to the Tower's conscription methods.
Karthain does its best to suppress knowledge of this organisation, but its name appears throughout histories concerning slavery. It remains a clandestine organisation by necessity. The Sable Tower has a standing bounty on information leading to the arrest of members of the Chain. Members are recruited carefully and organised into cells. The rumoured head of this organisation is titled Sanguine Illuminator.

The Chain's odd name comes from an old method of freeing slaves. A Bloodlantern was the name of an alkhamical lantern that would grow hotter when blood was fed to its flame. These lanterns are now rarely made. So hot would these lanterns grow that they could make low-quality metals weak, breakable. Chains were broken, and often used as weapons against former masters.