Hydra Cordatus is a harsh and arid world, remarkable chiefly for the mighty fortress-citadel raised upon it to guard a precious cache of the Imperium's treasures. Its bastions of rockcrete and adamantium, the Citadel and the outlying redoubt of Tor Christo, were held by the Imperial Guard of the Astra Militarum against foes that would have broken lesser defences in a single night.
The world earned its dark renown when the Iron Warriors, master siegecraftsmen among the Chaos Space Marines, descended upon it in overwhelming force. For long and bitter months the defenders held the walls against relentless bombardment, tunnelling, and assault, their courage a thing of legend even as their numbers dwindled. In the end the fortress fell, its walls broken and its defenders slaughtered, for no valour could withstand the grim patience of the Warsmith and his legion.
Though the siege of Hydra Cordatus ended in tragedy, the defenders' stand became a byword for the price of duty in the 41st Millennium. The world's fortifications, so painstakingly raised, were reduced to rubble and its garrison to corpses. Yet the Imperium remembers, and the name of Hydra Cordatus is spoken still as a testament to those who hold the line to the last, though the darkness swallow them whole.