Cut a giant in half, despite armor

At the last Arthur became enraged, and he called to him all his strength: and boldly angry and swiftly resolute and furiously determined, he lifted up his sword and struck Rhitta on the crown of the head a blow so fiercely-wounding, severely-venomous and sternly-smiting that it cut through all his head armour and his skin and his flesh and clove him in twain.

The Mantle of King's Beards