First appeared in Weird Tales, November 1932.
Rome. What his name or his rank, I do not know. I do not care. He might have been a faithful unknown warrior of mine, he might have been an outlaw. I only know that he was mine; the first scents he knew were the scents of the heather; the first light he saw was the sunrise on the Pictish hills. He belonged to me, not to Rome. If punishment was just, then none but me should have dealt it. If he were to be tried, none but me should have been his judge. The same blood flowed in our veins; the same fire maddened our brains; in infancy we listened to the same old tales, and in youth we sang the same old songs. He was bound to my heartstrings, as every man and every woman and every child of Pictland is bound. It was mine to protect him; now it is mine to avenge him."
"But in the name of the gods, Bran," expostulated the wizard, "take your vengeance in another way! Return to the heather--mass your warriors--join with Cormac and his Gaels, and spread a sea of blood and flame the length of the great Wall!"
A Pict king swears revenge on the Roman governor of Eboracum (York) after the governor crucifies one of his subjects. The revenge involves enlisting the help of monsters of the underworld.
The monsters are never completely seen or described, they're just horrible and give off bad vibes.
An okay story, the setting is unusual--England during the Roman occupation, before the Vikings, Anglo-Saxons, and Normans swept through.
One of Howard's best. Genuinely creepy and otherworldly. It's short, give it a read and see for yourself!