elanya

Glad you asked :) The monarchy rotates through six Houses, which are not really families, but huge extended, vaguely-related groups (phratries, I believe, is the technical term ;) So, the current Emperor is from the House of the Bear. After he dies, the House of the Lizard gets their turn.

While in theory anyone at all from the House of the Lizard could be the next ruler, in practice it doesn't work quite that way. First, the oldest and more prominent members of the House of the Lizard gather together to pick a short list of candidates. These will almost always be young, bright people chosen from one of a dozen or so traditional noble families. Once that short list is in place (and obviously any of them could back out if they wanted), the real fun begins.

Each potential Emperor or Empress must pass through The Arch. This is an ancient, mystical artifact of unknown power and nature. In some not-entirely-clear way, the Arch evaluates or tests each candidate. Those who are found unworthy are driven insane or killed on the spot. Out of those who aren't (assuming there are some ;), one person will be selected by the Arch (again, in some mysterious way) to rule. They are 'marked' in this process (the nature of the mark reputedly varies from person to person). If no one passes the test, the process begins again until a suitable candidate is found. :)