Second paragraph of first entry under C ("Caldera"):

In itself the caldera wouldn't appear to be a remarkable site. Though now covered over, at first glance it would seem to be little more than an absence, where the Yssgaroth incursion ate away all local matter and the Houses later surrounded the area with defences and utilities of their own devising. But its position is key. Anything exert-ing an influence on the site of the caldera will, by definition, affect the rest of history. It's the focal point not just of time but of the Houses' culture: as the Protocols of the Great Houses are worked into the very nature of history, coded into every one of the "threads" which criss-cross the Spiral Politic, then more than any other location the caldera is the centre-point of all that the Houses know and all that the Houses are. Theoretically, from here everything about the Houses – their past, their future, their collective memory, even their language – could be manipulated. The Houses themselves have never risked any significant experimentation, but during the War Era at least one abortive attempt was made to introduce foreign matter to this empty space at the heart of the oldest civilisation. That the site might be vulnerable is a constant worry to the ruling Houses, something which may have been a factor in the decision to construct the Nine Homeworlds shortly before the War began.

The first in the series of Faction Paradox Doctor Who spinoff books, this is supposedly an encyclopedia of things in the Faction Paradox world which sort of comes together to make a story or several stories (an approach also used by Christopher Priest in The Islanders). I admit I did find it all pretty confusing, but it was engaging enough that I've got hold of the next few volumes in the series and will start getting through them at the rate of one a month for the next while. This is not easy to get hold of.