During the Horus Heresy, Heta-Gladius was one of the many key worlds on the route to Terra fortified by Rogal Dorn in the prelude to the Siege of Terra. By the later stages of the Heresy, the world was protected by five Star Forts, 20 picket ships, Blood Angels and Imperial Fists, and a Imperialis Armada battlegroup. Due to a Warp-surge, the Vengeful Spirit and its escorts plunged from the Warp as it was on its way to the traitor muster at Ullanor and right within the range of Heta-Gladius's guns. With Horus indisposed following the Battle of Beta-Garmon, Horus Aximand stubbornly led the small Sons of Horus force against the formidable Imperial defenses at Heta-Gladius. In a battle that saw the Vengeful Spirit boarded by Blood Angels, eventually Maloghurst was able to restore Horus in time to resume command of the Legion and disengage from Heta-Gladius.