Worms of the Earth
by Robert E. Howard
Bran Mac Morn, king of the Picts, vows to take revenge on the Roman governor Titus Sullu after witnessing the crucifixion of comrade Pict. He seeks forbidden help from the Earth's Worms, a race of creatures that were once human, but have become terrifying and half-finished living underground for generations. After stealing his religious objects from the mound, he provides their help and exchanges them back in exchange for delivering them to him for a battle to the death. However, Sulla's mind breaks out of contact with the monstrous Worms of the world, and Bran Mac Morn mercifully kills him instead of taking revenge, realizing that some weapons are too bad to be used even against Rome.
