A Circle helps a wizard refine his magic, focus and direct it more clearly. It creates a sort of screen; defined by a perimeter keeping random magical energy from going past it. It can be drawn on the ground, made by several people holding hands, or a number of other methods. Then it's invested with a bit of energy to close the circuit.
Methods to draw a circleEdit
Draw a Circle, then put a drop of own blood on the circle, and imagine a wall going up. Chalk works but various things can be used to make the circle itself: marker, pouring dirt or powder, etc.
Walking slowly clockwse around a circle fashion is called deosil and is done to gradually power up the circle.
Circles create boundaries that isolate an area inside from the magical energies of the world outside.
Circles are an effective and standard way to trap a spirit, making it helpless to leave or use power. A circle made of fire can destroy the spirit.
A Greater Circle is a very powerful form of a circle used to contain a person or being with incredibly powerful magic, such as the Archive. It requires an enormous amount of steady, powerful energy. Hellfire is powerful but very unstable flowing in starts and sputters. To hold a Greater Circle of long periods would require the kind of power found in Ley lines.
Learning how to properly establish a Circle is the first thing any apprentice is taught.
The integrity of a Circle as part of ritual magic is most important. Any object that falls across it or breaks its plane would collapse the circle energy. Dust wouldn't collapse it but it would degrade its efficiency.
In the seriesEdit
- Main article: Storm Front
In Storm Front, Harry puts himself and Susan Rodriguez inside his brass circle in his lab and wills it closed, just in time before the Toad Demon spits acid at him which splatters against the circle's barrier. Susan had just taken a love potion by mistake and it starts to take effect while they are inside the circle, and one wrong move will break the circle. 
- Main article: Grave Peril
In Grave Peril, in his lab's copper Circle, Harry attempts to summon Azorthragal who was the Demon that Leonid Kravos made efforts to secure as his servant. Harry ends up summoning the Nightmare instead, assuming Azorthragal is the Nightmare.
- Main article: Summer Knight (novel)
- Main article: Blood Rites
In Blood Rites, Harry enlisted Jake Guffie to help with setting up circle around Arturo Genosa's studio to block the Malocchio curse. Jake assumes Harry is doing some sort of feng shui, and Harry agrees that it is. Later, Trixie Vixen told Harry that she had watched him make it and then broke the Circle when he wasn't looking.
- Main article: Dead Beat
In Dead Beat, Harry told Waldo Butters that a Circle can stop zombies by cutting off the flow of energy from the necromancer controlling them. Harry taught Butters how to make a Circle around himself to block the magic emanating from the Cowl's storm making so that he could power-up the GPS system they plan to use to locate the Word of Kemmler]]. During a Specter attack near the Darkhallow site, Butters empowered a circle around himself, protected from the Specters, he kept up a steady beat for Sue.
- Main article: Proven Guilty
In Proven Guilty, with seconds left of consciousness, Harry drew a circle in the dirt around himself while he was being choked by the severed hand of the Scarecrow, cutting off the power connection to the Scarecrow and allowing him to breathe again. The hand turned to Ectoplasm.
- Main article: Small Favor
- Main article: Turn Coat
In Turn Coat, Harry draws a circle around Murphy and himself when they are surrounded by Grey Suits. The repeatedly attempt to enter the circle by bumping up against it then by pressing their palms—which had mouths containing sharlklike teeth, purplish-black tongues, and yellow mucus—against the circle. Then, Molly Carpenter draws a circle around Binder's minions, the Grey Suits, at Donald Morgan's suggestion, which cuts off the flow of energy they needed to maintain solid forms. They suddenly melted into transparent ectoplasmic gook. 
- Main article: Changes
In Changes, Harry activates his Speaking stone, (aka Sending Stone) to ask Ebenezar for help from the Grey Council is locating where the Reds took Maggie, his daughter. Ebenezar cuts Harry off before he can tell the child is his daughter and scolds Harry for thinking only of one child and not the millions of children that the White Council protects from the Reds.
After blanking out with Ebenezar McCoy, Harry summons a multitude of nature spirits, water spirits, and messenger spirits from the various realms in the Nevernever. And servants of the Tylwyth Teg whose king Harry is on good terms with. Even a sentient flame creature who communicated in images. One of the fire spirits showed Harry an image of Maggie shivering in fear or cold, reaching out for a flame for warmth. Later, while Harry was lying with a broken back in Saint Mary of the Angels alone in the dark, he forms a Circle in his mind to summon Uriel and then Mab.
- Main article: Ghost Story
- Main article: Cold Days
In Cold Days, Harry seals a Circle of black pepper he poured from a shaker around Thomas's phone. Then he hexes all of the electronics in Thomas's apartment—the phone is protected from the hex to remain usable—then Harry breaks the Circle. This spell hexed all of the bugs that Lara Raith regularly places around Thomas's apartment. Harry's ulterior purpose to hexing the bugs was to alert Donar Vadderung as to how Lara operates when her operatives follow-up on Harry's call to him. Harry calls it a "friendly gesture", Thomas suggests it was a payment for meeting him.
The Ladies of Faerie, Lily and Maeve, made an enormous powerful circle that tapped into Demonreach's basic architecture. Only Harry was able to enter and he had to do so naked. The Ladies were attempting to wear down the defenses of the Demonreach Entity to release what is underneath it. Harry's friends figured out how to pass through the wall of the circle—by covering themselves with mud, they fooled it into identifying them as part of the island and so ignoring them. Harry used that Circle to summon Mab. 
- ↑ 1.0 1.1 Blood Rites, ch. 25
- ↑ 2.0 2.1 Storm Front, ch. 6
- ↑ 3.0 3.1 Dead Beat, ch. 36
- ↑ 4.0 4.1 Changes, ch. 29
- ↑ Storm Front, ch. 8
- ↑ Fool Moon, ch. 7
- ↑ Changes, ch. 9
- ↑ Ghost Story, ch. 11
- ↑ 9.0 9.1 9.2 Turn Coat, ch. 19
- ↑ 10.0 10.1 Ghost Story, ch. 15
- ↑ 11.0 11.1 Dead Beat, ch. 6
- ↑ Small Favor, ch. 39
- ↑ 13.0 13.1 13.2 Changes, ch. 19
- ↑ Storm Front, ch. 13-14
- ↑ Grave Peril, ch. 23
- ↑ Summer Knight, ch. 19
- ↑ Blood Rites, ch. 24
- ↑ Dead Beat, ch. 39
- ↑ Proven Guilty, ch. 22
- ↑ Small Favor, ch. 42
- ↑ Changes, ch. 30
- ↑ Cold Days, ch. 20
- ↑ Cold Days, ch. 46
- ↑ Cold Days, ch. 50
- ↑ Cold Days, ch. 51