The Castellan Rhino was an ancient specialised siege variant of the Rhino APC and was used solely by the Iron Warriors Traitor Legion. The Castellan Rhino was designed by the Iron Warriors' Primarch, Perturabo, for use during siege warfare. The Castellan Rhino featured unfolding armour plates and impact bracing that turned them into miniature bunkers, whose modular construction allowed the Castellan Rhinos to be linked together in a chain, forming a makeshift fortified line when materials for more permanent emplacements were unavailable or a defence had to be fashioned quickly.
During the Great Crusade and the Horus Heresy, the Iron Warriors would deploy many, sometimes thousands of Castellan Rhinos to encircle fortifications and cities quickly. During the Iron Warriors and Emperor's Children's siege of the ancient Eldar fortress of Amon ny-shak Kaelis the Iron Warriors deployed over 400 Castallen Rhinos as their defensive line. Current Imperial records do not indicate which Pattern of Rhino APC was used for the Castellan variant, although both the Deimos Pattern and the standard Mars Pattern Rhinos were used by the Iron Warriors during this era.
- The Horus Heresy: Book Three - Extermination (Forge World Series) by Alan Bligh, pg. 127
- Angel Exterminatus (Novel) by Graham McNeill, pp. 221, 282, 287, 290, 292, 300, 282, 289, 290, 388, 412, 417, 436-437, 466-46