The Duel with Hrungnir

Odin started it, as usual. Out on Sleipnir, he fell to boasting with a giant he met on the road — Hrungnir, who kept the best horse in Jötunheimr, a gold-maned stallion called Gullfaxi. No horse could touch Sleipnir, Odin said, and rode off before the giant could argue, which was argument enough. Hrungnir mounted up and gave chase in a fury that carried him straight through Asgard's gates before he noticed where the race had taken him.

By the old law of the road, a guest who arrives even in anger is a guest, and the Æsir gave Hrungnir ale rather than a fight. It was a mistake measured in horns: drunk, alone among his enemies and feeling invincible for it, he began to boast louder than a guest should — he would drink all their ale, he would sink Asgard itself, he would kill every god but keep Freyja and Sif for himself. Hospitality has limits. The gods sent for Thor.

What is a hólmganga?

Thor arrived hammer-in-hand and ready to end it on the spot, but Hrungnir pointed out, correctly, that he was unarmed and under the gods' own roof — no glory in killing a defenseless guest, and worse, a breach of the very hospitality law that had let him in. So the two agreed to something the mythology had never needed before: a hólmganga, a formal duel fought on appointed ground, with seconds, witnesses, and a fixed hour, rather than a killing in a hall. They set the field at Grjótúnagarðar, on the border of the giants' country, and each side prepared.

The giants took their champion's honor seriously enough to build him help. Fearing Hrungnir could not stand alone against the thunder-god, they raised a second warrior out of clay — Mökkurkálfi, nine leagues tall and nine leagues wide, given a mare's heart because no ordinary heart was big enough to fit inside him and no giant's own would serve. He looked magnificent. He had never fought anything in his life, and it showed the instant he saw Thor coming.

The exchange at Grjótúnagarðar

Hrungnir stood his ground with a shield of stone held before him and a whetstone for a weapon — the giants' version of a spear, an unglamorous rock meant to be thrown hard enough to matter. Before the fight began, Thor's companion Þjálfi ran ahead with a piece of useful disinformation: the god was coming up from below, through the earth itself, so a shield on the ground would do no good. Hrungnir, believing it, stood on his shield instead of behind it — stone under his feet when the attack that mattered came from the sky.

It came in lightning. Thor arrived roaring and Hrungnir hurled his whetstone to meet Mjölnir in mid-air. The two weapons met head-on: the hammer shattered the whetstone into fragments, one half burying itself in the ground to become, the myth says, the source of every whetstone-vein since, and the other half driving straight into Thor's skull, where it lodged. Mjölnir did not stop for the collision — it went on through the whetstone and into Hrungnir's stone head, breaking his skull to pieces and dropping him dead across the field. Beside him, Mökkurkálfi's brief and glorious career ended in the same minute; Þjálfi felled the clay giant, who went down, Snorri notes dryly, "with little glory," his mare's heart no substitute for nerve.

Why does Thor still carry a whetstone in his head?

Victory came with a complication. Hrungnir's corpse fell with one huge leg across Thor's neck, pinning him to the ground, and not one of the assembled gods — not even Odin — could shift a dead giant's leg off their strongest. It took Thor's own three-year-old son, Magni, born of the giantess Járnsaxa and already showing his father's strength before he could properly talk, to lift the leg away and free him. As a reward Thor gave the boy Gullfaxi, Hrungnir's own horse — a gift that reportedly needled Odin, who felt the prize-winning horse should have gone to the god who had provoked the whole race in the first place.

The whetstone shard, though, stayed. Thor carried it in his head afterward, and the one attempt to remove it very nearly succeeded: a sorceress named Gróa, whose magic could loosen stone from flesh, sang the fragment nearly free while Thor sat and let her work. Grateful — and unable to help himself — he told her, mid-spell, some welcome news he was carrying: her long-lost husband was making his way home at last. Gróa forgot every word of her charm in her joy, and the shard settled where it was and never moved again. Norse tradition drew a household superstition straight out of the wound: never throw a whetstone carelessly across a floor, because the fragment in Thor's skull is said to stir when you do.

In the primary sources

The fullest account is Snorri Sturluson's Skáldskaparmál, in the Prose Edda, told to explain kennings for Thor built on this fight — "Hrungnir's-skull-splitter," "slayer of the stone-giant." Snorri draws heavily on the ninth-century skaldic poem Haustlöng, by Þjóðólfr of Hvinir, which survives only in the quoted stanzas Snorri preserves, and which already describes the mid-air clash of hammer and whetstone in vivid, compressed verse — proof the story was old and well-known centuries before Snorri wrote it down.