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First Siege of Hydra Cordatus

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First Siege of Hydra Cordatus
Location of Hydra Cordatus
Conflict Horus Heresy
Date ~007.M31
Location Hydra Cordatus
Outcome Iron Warriors victory
Iron Warriors Imperial Fists
Primarch Perturabo
Warsmith Forrix
Warsmith Harkor
Warsmith Soltarn Vull Bronn
Warsmith Barban Falk
Warsmith Toramino
Lieutenant Kroeger
Siege Captain Ascari Valkar (KIA)
Captain Felix Cassander(POW)
Space Marine Legion 200 Imperial Fists
Thousands of Human auxiliaries
Mechanicum forces
Heavy All killed or captured

The First Siege of Hydra Cordatus was a battle during the Horus Heresy. The assault on the world of Hydra Cordatus was undertaken by the Iron Warriors led personally by Perturabo, who was targeting the worlds small Imperial Fists garrison. Due to the fierce rivalry and mutual hatred between both Legions, tensions ran high. The primary target for the Iron Warriors was the world's Cadmean Citadel.

After a fierce orbital bombardment by Magma Bombs, the Iron Warriors landed but found the defenses of the Cadmean Citadel formidable. As a result, the Iron Warriors were bogged down into a 3 month siege. Inside the citadel, tens of thousands of normal humans as well as women and children were being provided shelter by the Imperial Fists. Nonetheless after 3 months Perturabo had enough, and led a final charge that saw the Primarch kill the remaining Imperial Fists and break the defenders. Most of the Imperial Fist were massacred while the human refugees were all butchered or enslaved. Hydra Cordatus became a barren wasteland.


No one knew who built the Cadmean Citadel, and the fortress had the ability to automatically repair damage that was inflicted to its structure by pouring liquid silicates that would fill any wounds. The wall had other defenses including the ability to form spikes that would pierce any invaders or it would open gaps and cover an attacker.[1a] Beneath the wall were gravity generators that slowed anyone would who attempt to climb, but their range was limited to only a few meters.[1b] The Mechanicum performed extensive research on the facility but could not understand how it worked. The fortress was not invincible; it could be damaged to an extent in a short period of time that made it irreparable, overwhelming its mechanics. Neither the material nor the technology came from Hydra Cordatus.[1a]

The Imperial Fists brought the world to compliance during the Great Crusade, and Rogal Dorn made the place a capital so that the people would have an ordered government. They elected Endric Cadmus as their planetary governor, and iterators and remembrancers were spread to promote the Imperial Truth. Captain Felix Cassander of the 42nd Company and two hundred legionaries were stationed on the planet as the legion departed to continue their conquest. Eventually, Dorn ordered all Imperial Fists to return to Terra, but the death of Cassander's navigator made that impossible. Before a replacement could be found, he received word that Horus turned traitor[1a]


The Iron Warriors began their invasion by bombing the valley and surrounding areas, destroying the land, before landing legionaries, guns, and other equipment for a large scale siege. The Imperial Fists gave nicknames to the four commanders of the Iron Warriors based on their actions: Scrapper (Triarch Harkor, who led assaults), Digger (dug fortifications to bring in artillery), Malingerer (used artillery from afar), and Voyeur (Triarch and First Captain Forrix, who watched from the valley center).[1a]

Over the three months period since the start of the battle, 3/4th of the Imperial Fists were killed, including Techmarine Scanion, and thousands of the Imperial soldiers were killed. The Iron Warriors were making a slow advance towards the fortress, building trenches and defensive emplacements for their guns. During this time, Perturabo spoke to very few of the Iron Warriors, preferring to speak through the "Stonewrought" (Soltarn Vull Bronn). Vull Bronn was of the 45th Grand Battalion, and his ability to understand stone brought him into the favor of the primarch even though he was not a captain.[1a]

Battle for the Cadmean Citadel

With the Iron Warriors' 33rd Grand Battalion at his command, Iron Warriors Siege Captain Ascari Valkar attacked the Cadmean Citadel, alongside the Tyranthikos. Despite the efforts of the Imperial Fists' 42nd Company, Mechanicum and the Chalchidean Grenadiers Solar Auxilia, the Iron Warriors succeeded in breaching the Citadel's outer gates. However they were then attacked by an Imperial Fists Forge Lord, who commanded five maniples of Castellax Robots. Their firepower took a toll on on the Battalion and the Iron Warriors would have been pushed back had the Tyranthikos not charged into Robots. This allowed the Iron Warriors to regain their footing, but the battle then entered a bloody stalemate. Both sides began taking serious losses, but Valkar called for more reinforcements to defeat the Imperial Fists. However, with two thirds of the 33rd Grand Battalion dead or grievously wounded, Galan Dion and the Tyranthikos could see that the Siege Captain had failed. In order to safe what was left their combined forces, the Veteran decided to remove Valkar from command. Valkar saw them coming, though, and the Siege Captain was able to keep them at bay with his power sword. Dion was finally able to disarm him by shoving Valkar to the ground and this allowed the Tyranthikos to bring the Siege Captain to their waiting Primarch. Valkar was given no chance to account for his failure and, on Perturabo's order, the Iron Circle Domitar Robots turned the Siege Captain into bloody pieces.[2]

Final Attack

Forrix admired the structure of the Cadmean Citadel and how the Imperial Fists transformed the area to turn them into liberators and not conquers, which the Iron Warriors would never bother to do. He turned to Warsmith Barban Falk, who was angered by the sentiment because of the disastrous results that took place at the Battle of Phall. They moved on to discuss the final attack on the western approaches, and Falk favored relying on more legionaries than extra siege batteries. Forrix questioned an assault, noting that mines could be emplaced, but Falk said that the "Stonewrought" (Soltarn Vull Bronn), speaking for the primarch, assured that there would be none in that region. They were interrupted by the sound of an assault taking place on the north by Harkor's warriors.[1]

By the moment of the final attack, Cassander only had 51 legionaries, and there were over 13,000 remaining citizens in the fortress who would easily be slaughtered if the defenses were breached. Cassander was realistic and knew that a last stand would not be glorious. He stood on the northern side of the fortress with Locris and Kastor, noting that the pace of the Iron Warriors dramatically increased. They believed that it was Scrapper and not Digger, who was attacking: the Iron Warriors were trying to climb up mountain to the wall, moving ahead of their guns on walker platforms, and they were motivated by great hate.[1a]

Locris pulled a trigger and detonated mines in the slope that destroyed a 300 meter section that crashed down on the Iron Warriors. Cassander then had Symeon, Esdras, and Phyros redeploy to the north to defend against the remaining assault force.[1a] Iron Warriors Lieutenant Kroeger pushed on through the gravity trap and quickly forced himself up the wall, climb with only a few of the toughest legionaries while the 300 others of Harkor's 23rd Grand Battalion set up weapon emplacements or took cover. Servitor weapon emplacements blasted the Iron Warriors as Imperial Fists shot down the wall. The Iron Warriors were forced to stop their fire to prevent hitting their own troops. Khamer, Ulgolan, Purdox, Straba, Vannuk and many other Iron Warriors were killed in the attempt. This enraged Kroeger further, and he managed to reach the top with two others, Vortrax and Ushtor.[1b]

Surprising the Imperial Fists, Kroeger managed to hit Cassander in the head but did not kill him. Vortrax was soon killed as were Imperial Fists, and two more Iron Warriors reached the top. Cassander charged the two new Iron Warriors and killed them before challenging Kroeger, who was now alone, but Kroeger instead shot him twice in the chest. Before Kroeger could kill another Imperial Fist, over 20 other Imperial Fists arrived and blasted him in his side, hitting him multiple times before he could take cover. His arm was damaged and his bolter destroyed. Before he could bleed out, a stormbird hovered above the top of the fortress, killing many with its engine wash as Perturabo landed with the Iron Circle.[1b]

Perturabo made short work of the defenders. The Imperial Fists immediately turned to attack the primarch, but he made slaughtered them easily. After killing them, the primarch then smashed Forgebreaker into the stone rampart. Perturabo then went to Kroeger, who was barely alive, and commanded the legionary to remove his helmet. The primarch then said that he remembered Kroeger then asked where his warsmith was, to which Kroeger said he was "with the guns". Perturabo remarked on Kroeger surviving the attack alone, ignoring his fellows who died at the top, then examined Kroeger with his immaterium senses. Harkor appeared via thunderhawk along with others, including Forrix, Falk, and Toramino of the Stor-Bezashk They approached the primarch cautiously, wary of his rage, and knelt before him.[1b]


Harkor believed that he would be honored for finally breaking the fortress. Instead, the primarch was oddly silent, unsettling the warsmiths, until he spoke, asking if he was clear in his orders. Before Harkor could respond, Perturabo grabbed his throat and lifted him with ease. The primarch expressed his anger at not being obeyed, but Harkor tried to say that he saw an opportunity and tried to take it. Perturabo responded that victory was not from Harkor. Instead, he turned to Kroeger and pointed out that he alone survived the assault, the others wasted as Harkor hid in protection. Instead of killing Harkor, Perturabo ripped off Harkor's armor with ease, deeming him unfit to wear the armor and labeling him as rust.[1b]

Harkor was stripped of his status as a triarch, of which Forrix was glad because he never supported Harkor in the position. He was returned to the status of normal legionary of the 23rd Grand Battalion and was dismissed. Perturabo then stated he needed to find two replacements, Erasmus Golg having died at Phall, and both Falk and Toramino stood and said they were ready to serve. The primarch asked Forrix for his recommendation. Forrix thought of suitable candidates that were no longer there, Dargron died at Phall and Varrek was sent to an unknown location, but stated that Falk and Toramino would be good. The primarch said he would normally agree, but today was different; he chose Falk and Kroeger instead. Perturabo also elevated Kroeger to commander of the 23rd Grand Battalion.

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