Guilliman's Gate is the entrance gate that leads from the surface of Calth to the vast underground caverns where the planet's population dwells[1a]. Because of Calth's reduced and polluted atmosphere, the intense solar radiation that reaches the planet's surface is lethal to all forms of life[1b].
As the only way in or out of Calth's inhabitated underground, Guilliman's Gate is naturally heavily fortified and defended. It is also richly ornamented with statuary, including a colossus of Remus Ventanus, the hero of the Ultramarines who led the defense of Calth during the Horus Heresy[1a].
During the Bloodborn's Invasion of Ultramar, Warsmith Honsou personally led a force of Iron Warriors to Calth. Seeing Guilliman's Gate, he quickly discerned that it was impenetrable to any conventional assault, even for experts in siege warfare like the Iron Warriors. Instead, the Gate's defenses were penetrated by a small team of expert climbers and close-combat specialists, including Ardaric Vaanes, The Newborn, and a small force of loxatl mercenaries. This team entered the Gate through an open gun port, overpowered the gunnery crew, and, with The Newborn's inside knowledge, overrode the command codes and opened the Gate, letting Honsou's army in[1c].
- 1: The Chapter's Due (Novel) by Graham McNeill: