Binding circles are a kind of rune magic that targets either a certain species of being or a specific being altogether, depending on the exact runes used in making it. The being that is to be bound needs to be within the circle, obviously, and the binding circle is only effective for as long as someone is supplying it with a continuous flow of magical energy to fuel it. Anyone caught in an active binding circle that is targeting them has their ability to use magic drastically reduced, often to the point of removing it entirely, as well as physically weakening the target and preventing them from leaving the circle for as long as it remains active. The more reliant one is on magical energy, the more one is affected by the circle, so generally beings primarily composed of magical energy, such as undead and immortals, are extremely susceptible to them. The stronger an entity one is trying to bind, however, the more energy the circle is going to require in order to bind it.