The Guild of philosophers who inhabited the tower created Æsahættr. They used the knife to cut into other worlds, each time unknowingly creating a Spectre. The Spectres invaded Cittàgazze and the tower, just like the town, was abandoned. The Subtle Knife, which repelled Spectres, was kept in the tower by Giacomo Paradisi.  
Torre degli Angeli is Italian for "tower of the angels."