Vortigern Timeline and Summary

Vortigern meets with the lesser kings of Britain to shore up his support against his enemies—who are many.
Vortigern faces a revolt led by his son Vortimer & Friends and successfully suppresses it.
Vortigern sends his henchmen to find a lad who has no earthly father (i.e., Merlin) to sacrifice for his tower's walls.
Vortigern also summons Niniane to confirm that Merlin's father is, in fact, a demon.
Vortigern and company head out to the ruins of the tower so that Merlin can figure out the problem—or be sacrificed if he can't.
Vortigern follows Merlin down into the mineshaft under his tower and sees the pool. Merlin prophesies for him.
After seeing the signs of the two dragons, Vortigern takes Merlin's advice and flees.
Vortigern shuts himself in Doward Castle to face Ambrosius. He (or Rowena) has Ambrosius' messenger mutilated.
Ambrosius burns Vortigern to death in his castle.