The Subtle Knife
It is in Cittàgazze that the two central characters, Lyra and Will, first meet in "The Subtle Knife". The first reference to the city appears earlier, as 'the city in the sky', the city visible in the "Aurora borealis", an occurrence which, according to the novel, thins the barrier between the universe in which "Northern Lights" takes place and the universe of Cittàgazze. Lord Boreal describes it as having previously been a crossroads between all the worlds.