The Savage Sword of Conan #178

The Nemedian Imperator Addelaus, a noble's son, is captured by Hyperborean savages who take him to a tower called the Pillar of the Sky to be sacrified to the sky god Bardisattva. Conan and a small group of soldiers embark on a rescue mission but find Addelaus driven mad by torture administered by the priests known as the Silent Followers.