The Thongor books helped reestablish the sword and sorcery genre in the 1960s. This is a classic.
Publisher blurb: "Xothun had ruled in Omm for a thousand years -- master of strange powers, yet slave to his craving for human blood. The lost city lived only to serve -- and feed -- Xothun.... Then came the barbarian adventurer, Thongor of Valkarth, with a city to free, a princess to rescue, glory to win -- and his mightly sword to pit against Xothun's wizardry!"
Series: Thongor: Book 2