So basically we have an enormous clue and chekhov's gun. In the scene where the Outsiders target Eb and Harry (more on that in another thread), Eb suggests a quasi-legal technique that is mostly associated with black magic - the Ring of Fire.
Harry explains it as an experimental fusion reactor. All the energy in the ring of fire bounces back in on itself getting stronger and stronger until it achieves it's effect or explodes (with something like the force of a small nuke). Largely this seems to be because the technique involves a circle of will (so like normal, infused with a drop of mortal blood) combined with fire. Real fire being stronger than sorcerous fire (more on that in another thread). The combined effect is incredible, clearly. But also very, very dangerous.
My guess is that this technique is something we will see much more of in the series, especially associated with the Circle. In fact, I suspect it is some metaphor for what they believe in (hence the name).
See, the Circle seem to believe in Power without restraint (as evidenced by their Sign, also used by Kemmler's forces and the Thule Society). This also ties into some sort of link to the Denarians and Hell, but to that I am not sure. I suspect that is part of the reason why fire was used in the capturing of the Archive. Perhaps it is a combination of the Ring of Fire, the blood, the pentagram/pentacle (with it's points being outside the circle) that make it so powerful.
