Talk:Thirteen/@comment-210.215.131.89-20160303024517/@comment-26247132-20160303031720

People born with black blood are sent to Polis to be trained to become the next Commander. When the current Commander dies, a "conclave" is held and one of the Nightbloods is chosen to become the next Commander in some way. Maybe it's like choosing the next Pope, maybe it's Hunger Games style; we don't know yet.