Percepton

Percepton was a world of the Ultramar sector drawn into the Word Bearers’ war against the Ultramarines during the Horus Heresy. Its exact location within Ultramar is not precisely attested, though it lay within the broader theatre of operations affected by the Word Bearers’ betrayal at Calth and the subsequent Shadow Crusade waged by Lorgar’s Legion across the Ultramarines’ home sector.

Following the massacre at Calth, isolated Ultramarines formations found themselves cut off from Guilliman’s main forces and forced to continue resistance with limited resources. On Percepton, this resistance took the form of a protracted underground conflict, as surviving Ultramarines personnel contended with Word Bearers elements amid the planet’s subterranean workings, far from the open battlefields more commonly associated with the Heresy’s major campaigns.

Percepton is remembered chiefly as an illustration of the fragmented, small-unit warfare that characterised the Ultramar theatre once the sector’s defences were thrown into disarray by the treachery at Calth, rather than as a site of strategic significance in its own right within the wider civil war.