From Edge of Darkness Wiki
Summoners p. 185
|Preq's||Sanctum (Size) ●|
Throughout the ages, willworkers have used bounded spaces to set their summonings apart from the outside world. In part, they do this for safety’s sake, but also to cultivate within themselves a sense of the gravity of the act, to separate this powerful form of magic from distractions, whether internal or external. Over time, many of these ritual spaces have become enhanced with their own uncanny character, sliding partway out of this world and partway into others.
A summoning circle must be attuned to a given realm (a particular Supernal Realm, the Abyss, Shadow, the Underworld, etc.); once set, this choice cannot be changed, though a mage may have more than one summoning circle (up to two at Gnosis 3, three at Gnosis 6, and four at Gnosis 9), with each corresponding to its own distinct world. For each dot of a single instance of this Merit, a willworker adds one die to all rolls to summon entities from the realm to which the summoning circle is attuned.
In other words, a mage with a one-dot summoning circle (Arcadia) adds one die to a summoning spell intended to call down an Arcadian spirit, while one with a three-dot summoning circle (the Abyss) adds three dice to any roll to call an Acamoth or Gulmoth. Note that the bonus dice only apply to attempts to summon the appropriate otherworldly beings, not to any dice rolls necessary to control them, forge pacts, or the like.Because of the sometimes delicate work necessary to properly maintain a summoning circle, one may only be constructed within a mage’s sanctum. A summoning circle can be part of a shared sanctum, but this Merit (and the structure that it represents) is personal in nature and may not be shared within a cabal.