A Cadian Pylon is one of a large number of massive pylon-shaped devices of unknown xenos origin erected millions of standard years ago in a complex network stretching across the surface of Cadia. These pylons can also be found on a number of other worlds close to the great Eye of Terror Warp rift in the Segmentum Obscurus. It is currently believed by the savants of the Imperium of Man and the Eldar Craftworlds that the pylons were erected over 65 million solar years ago by the Necrons during their ancient war with the Old Ones to serve as a defence against the psychic abilities of the Warp which are the Necrons' only real vulnerability. The pylons essentially act as anti-psychic field emitters, restricting the activity of the Immaterium in proximity to them.
The mysterious pylons of Cadia have stood since long before the coming of Man to this remote world. But their ultimate purpose remains a mystery. It is currently believed by the savants of the Imperium of Man and the Eldar Craftworlds that the pylons were erected over 65 million standard years ago by the Necrons during their ancient war with the Old Ones to serve as a defence against the psychic abilities of the Warp which are the Necrons' only real vulnerability. The pylons essentially act as anti-psychic field emitters, restricting the activity of the Immaterium in proximity to them. The Tech-priests of the Imperium's Adeptus Mechanicus have hypothesised that the pylons on Cadia exert some effect over the Immaterium, rendering it calm and creating the unusual zone of space-temporal stability known as the Cadian Gate, that enables ships to travel through the only known navigable route in and out of the Eye of Terror into realspace.
Recently, it has become clear to Imperial savants that the Pylons can be reduced to ruin by overloading their capability to hold the Empyrean at bay with massive amounts of Warp-spawned enemies, such as a massive incursion of daemons into realspace at one time. When the first signs of the coming Black Crusade began, as Warp Storm Baphomael expanded and began to engulf the edges of the Cadian System, of the 5,180 known intact pylons, at least 1,292 began to emit a psycho-temporal resonance. In the wake of the 13th Black Crusade in 999.M41, Abaddon the Despoiler intends to overload the Pylon network on Cadia itself to allow the Eye of Terror to envelop the worlds of the Imperium, allowing the Warp Storm to encompass the entirety of the galaxy. This outcome is known to the Forces of Chaos as the Crimson Path, for without the Cadian Pylons even Terra itself runs the risk of being swept up in the Eye of Terror.
The Cadian Pylons are massive structures of smooth black stone, 500 metres high and 250 metres square. The upper facing of each pylon contains holes and other round orifices about the size of a human head. The wind moves through these holes and often produces an eerie, mournful sound. These tubes through the structures are not straight. Mechanicus Tech-priests investigating the pylons have attempted over the centuries to run Servitor probes through them to map the structures but these probes usually did not return. There are 5,810 fully intact pylons on the surface of Cadia and over 2,000 others that are partially ruined or buried relics. No two of the pylons are identical in design largely because the strange tubes that run through them each follow unique patterns that differ from pylon to pylon. Each one rises exactly 500 metres high and is sunk 250 metres below the planet's surface. The similar pylons on other worlds in the Cadian Sector near the Eye of Terror look identical to those found on Cadia's surface.
- Codex: Chaos Space Marines (6th Edition), pp. 19-20
- Codex: Eye of Terror (3rd Edition)
- The 13th Black Crusade (Background Book), pp. 14-15
- Eisenhorn (Novel) by Dan Abnett