The fortress, called Azkaban, absorbs the evil of its creator, who used it as a lair from which he captured Muggle sailors and tortured them to death. Eventually the place becomes infested with Dementors (Pm).
Ekrizdis creates Azkaban fortress
Date 15th Century
Certainty Stated in canon
Location in Canon Pm: Pottermore
Type of Event Wizarding world