The Fist of Horus is a divine combat magic spell that summons a huge magical fist (or sometimes just a blast of magic) that is able to knock down walls, break metal chains, or even topple giants.
Effects
This spell can be summoned and formed in different ways. One way is to summon it by the use of the divine word khefa, creating a magical fist that slams into the target. (This is only demonstrated in the crossover short story The Son of Sobek and is not explicitly used in the main Kane Chronicles trilogy.)
Another way is to tap into Horus' power by raising one's hand (without needing to utter a divine word), creating a magical fist that slams into whatever the caster extends his/her energy towards.
A final way is the same as the second but, instead of a magical fist being created, the Eye of Horus sigil burns against the target, which acts like it has still been punched by a giant fist.
The Kane Chronicles
The Red Pyramid
During the attempt to get inside Set's pyramid, Carter Kane uses the spell to slam a door shut, before sealing it. Later, he uses it against Set himself, in a moment of union with Horus through pure protective rage.
The Throne of Fire
At first, Carter has not been able to use this spell ever since he separated from Horus, who had been using Carter as his host. But during an escape, using a similarity with the war god's experiences, Carter is able to summon the Fist of Horus to blast a door open. He later realizes that tapping into a god's emotions is the key to divine magic, a key part of the plan to defeat Apophis.
Demigods & Magicians
The Son of Sobek
While trapped inside the petsuchos, Carter prepares to use the Fist of Horus to free himself but is inadvertently rescued by Percy Jackson. During the argument that follows, Carter accidentally casts the Fist of Horus and flings Percy into a nearby swamp. Carter initially thinks he killed Percy with the spell, but Percy survives (as he's a demigod) and the accident leads to a fight between the two that ends in a draw. After calming down, Carter apologizes for using the Fist of Horus on Percy, telling him it was really an accident.
The Crown of Ptolemy
In response to Setne's taunts, Carter summons the Fist of Horus and smashes Setne into the ground so hard with it that the magician is completely buried.