A Caul is a place of power used by Nephandi, usually within a Labyrinth of sorts. They are used to create more Nephandi.
Overview
Cauls usually appear alive, resembling a twisted placenta, a glittering pocket of flesh, or a gaping maw. They act as gates that either physically transport the user to Hell (or the Void) and back, or at the very least simulate such a trip. Entering a caul gives the impression of millenia of torture, which has the effect of either killing the user outright, or making the user hardened and depraved. If the user emerges relatively intact they will have been fundamentally and irreversibly changed; their Avatar will have been inverted focusing on Descent rather than Ascension, and their magic becomes Qlippothic. Stepping into a caul must be done voluntarily. Involuntary entrance of a gate almost always results in death. Some mages never reemerge from their Caul and there is no reported incident of a Sleeper surviving the trip.
The Nephandi come into existence in two possible ways: firstly, they can be created from regular mages through the use of the caul, or they are simply born with inverted avatars from a previous life (so-called widderslaintes).
References
- MTAs: The Book of Madness Revised
, p.38-39