“Of all of the Knights, some of the largest war machines still in existence, the Porphyrion and Asterius are among the most rare.”

Acastus Knight Asterius Datasheet, Forgeworld

The Acastus class is comprised of two variants; the more common Porphyrion and the much rarer Asterius. Both are true giants compared to their Knight brethren, even towering over Cerastus class Knights. Their chassis is protected by heavily armoured panels and a powerful ion shield making them impervious to all but the heaviest firepower. Their enhanced reactors provide vast amounts of power to their weapons systems, able to engage the enemy with devastating firepower. Acastus pilots are known by other chassis class pilots as “kin-killers” due to the manner in which they are used. The Asterius is fitted with twin ancient Conversion Beam Cannons. Designs so archaic that their loss is incomprehensible. Able to engage and destroy fortifications at extreme range, those cannons are equally at home sniping enemy Knights or even taking on Scout Titans from concealed positions.

My Acastus Asterius in WIP Malinax scheme

Basic Rules & Core Capability:

Rules for the Acastus Asterius are available online here from Forgeworld free of charge. The Asterius is available to be taken as an Engine of Destruction and is considered part of the Panoply of War – meaning you can comfortably run this in a Legiones Astartes army as a Lord of War choice.

The Acastus Class has a basic stat line of:


As with most of the Super-heavy walkers, this stat-line is at first glance fairly underwhelming considering the price of it at 545pts for the Asterius and 560pts for the Porphyrion. This is made worse by the fact that, at face value, the Leviathan Siege Dreadnought is slightly less well armoured (at AV 13/13/12) and has a 4+ Invulnerable save with 4 HP for c.320pts. This is mostly down to the fact that the Leviathan is very well written and pointed, and also down to the fact that at face value, you miss most of the things that make the Acastus class seriously dangerous.

As a Vehicle (Super Heavy Walker), the Acastus class use the Super-Heavy Vehicle rules for Shooting, Vehicle Damage and Catastrophic damage. Moving a full 12″ in the movement phase, their threat range is genuinely terrifying, allowing for deployment in cover and manoeuvring to fire in T1 with minimal concern. If it moves into or within difficult terrain you double the highest dice roll when making a difficult terrain test to determine the maximum distance in inches the model can move.

Additionally, they have the chance to perform Stomp attacks. This consists of D3 stomps and is made in addition to the Super-Heavy walkers normal attacks. Stomp occurs at Initiative 1 and does not enable you to pile in further at that step. Stomping does allow you to “stomp forward” but the model doesn’t physically move. Imagine it more as giant metal happy feet movements.

Close combat is made more effective by the fact that Vehicle (Super-heavy walker) causes Fear. If at the start of each Fight sub-phase, a unit is in base contact with the Acastus, it must take a Fear Test. If it fails, it fights with a Weapon Skill of 1 for the rest of the Fight sub-phase.

Even though the Acastus class does not mount dedicated melee weapons, it does have a further ability to cause damage. With Hammer of Wrath, when an Acastus charges in it makes one additional attack at Strength 10, AP -. As with Stomp, this occurs at a dedicated Initiative step, in this case Initiative 10, but does not confer a pile in move. If the target is a vehicle, the hit is resolved against the facing armour value.

With movement already benefiting from Vehicle (Super-heavy walker), the addition of a further sub rule for Move Through Cover improves it even more. Move through cover means that you roll an additional D6 when moving through difficult terrain and is not slowed by charging through it. This means when you’re moving through difficult terrain, you’re rolling 3D6 and picking the highest dice roll. Remembering that the Vehicle (Super-heavy walker) rule then asks you to double the roll value. Any model with Move Through Cover automatically passes Dangerous Terrain Tests. This means that your movement is pretty much ignoring any terrain issues that you run into.

Invincible Behemoth effectively means that when a Destroyed, Wrecked or Explodes! result is rolled against the Acastus, it inflicts D3 hull points instead. One sub rule of this is that any attacks or abilities that permanently lower the AV of the chassis do not affect it. This does not stop rules such as Lance working.

Relentless grants the ability to move and shoot Heavy, Salvo or Ordnance weapons as if they had remained stationary. In this case, Ordnance. They are also able to charge in the same turn those weapons have fired. This means that you have no issues with movement to enable shots on a different armour facing, or to improve a target picture.

Smash means that all of the close combat attacks are resolved at AP 2, with the exception of Hammer of Wrath unless it has an AP 1 weapon.

Finally, you have Strikedown. Any non-vehicle model that suffers at least one unsaved wound or passes one or more saving throws against an attack with this rule moves as if it were in difficult terrain until the end of its next turn.

This brings us to the end of the sub rules that are provided by Vehicle (Super-heavy walker). However we aren’t quite at the end of the basic rules for the Acastus-class.

All Knights are equipped with an Ion Shield. When it is deployed, and at the start of each opposing sides shooting phase, the controlling player declares the position of the the Ion Shield. This can either be front, rear, right side or left side. This grants the Knight a 4+ invulnerable save on that facing for shooting attacks only.

For Mechanicum, the rule Blessed Autosimulacra is the final basic rule. It if has suffered hull point damage, at the end of the controlling players turn roll a D6, on a 6, one lost hull point is restored. This ties in well with Magos and Arch Magos Dominus Battlesmith rule and even more so if they have a Machinator array.

Overall, the ruleset makes the Acastus-class quite the opposing force to deal with. The mere presence of one will force one of two deployment reactions; stand and fight or hide. The former will see you having to choose the greater threat to the Knight and direct the Ion Shield as such. Take the time to consider the likely plan of action as there’s no Armoured Ceramite on a Knight. Therefore they’re very weak to Melta. The final thing to consider on the shield facing is that the humble Lascannon will glance on 5 from the front, 4 from the side and 3 from the rear. With the prevalence of that weapon, especially on Fast Skimmer platforms such as Javelin Speeders the mentality of thinking a turn ahead will help keep it alive.

The core function of the Acastus Class is to bring firepower to bear, be it on their kin, fortification or individual targets. So, lets look at those weapons.

Primary Weapons Systems:

The Asterius is the lesser-seen of the two Acastus class Knights, both in the lore and on the table. This is down to the way the Conversion Beam Cannon operates. Firstly, this is a template weapon with twin-linked, each cannon counting as one individual weapon. This grants re-roll failed wounds and armour penetration rolls. This is important to remember as the weapon is Strength 10 at all ranges, but the AP and blast marker and effect is variable due to the way the weapon operates in calibration brackets.

Twin-Linked Conversion Beam CannonUp to 18″103Ordnance 1, Blast 3″
18″-42″102Ordnance 1, Large Blast 5″, Wrecker
42″-72″101Ordnance 1, Massive Blast 7″, Wrecker, Sunder

Realistically, you are wanting to position the Asterius as far back as possible, however on a normal 6’x4′ or even a congested Apocalypse table, your maximum will likely be a sweet spot of the second calibration bracket of 18″- 42″. That means you’re firing two Large Blast 5″ templates with Wrecker. Wrecker allows you to re-roll failed armour penetration against fortifications and immobile structures, such as bunkers and barricades, and add 1 to the rolled result on the Building Damage chart. It’s capable of putting the fear into an opponent who enjoys using fortifications or when playing a mission that relies on fortifications or immobile structures being captured or destroyed to score points.

Lets not forget the fact the Conversion Beam Cannons are Ordnance; this means that you’re rolling 2 dice when determining armour penetration and pick the highest result. This provides quite the bonus to anti-tank. If you play it right, and maximise the shooting range – you gain Sunder at AP 1 in a Massive Blast 7″.

Don’t forget Twin-Linked either. Oddly, the datasheet doesn’t mention it on the weapon profiles; but it does in the wargear section. The Conversion Beam Cannons use Blast templates; this means that when you apply Twin-Linked you gain the benefit of Twin-Linked Blast Weapons by being able to re-roll scatter and the 2D6 distance and Twin-Linked Template Weapons (because you’re still using a template) to reroll failed to wound or armour penetration rolls.

Rules extract from Mechanicum Army List Enhanced Edition. This text is repeated across all of the Enhanced Edition books.

The issue that underpins the Asterius occurs when you have enemies move within 18″. The AP drops to AP 3 and the blast size drops down to Blast 3″. However, lets remember that there is no Firing Calibration rule for the Asterius Conversion Beam Cannons. As a result, you have 12″ movement with plenty of ways to negate terrain affecting that movement. So, you’re only really constrained by the table size and your opponents cunning when it comes to maintaining the sweet spot of the second Calibration Bracket. Sure, infiltrators and Deep Strikers will inevitably cause concern, but that’s where the rest of your army comes in.

Conversion Beamer Cannons use antimatter to cause a subatomic explosion that literally disintegrates its targets. The Asterius carries some of the largest types known.

Secondary Weapons Systems:

The Asterius is the lesser customisable of the two Acastus Knights, really cementing itself as the long range anti-fortification, Knight sniping monstrosity with its secondary weapons rather than its primaries. Equipped with a plethora of anti-infantry weapons to complement the primaries, it can nonetheless create swathes of devastation with radioactive Karacnos Mortars and two Volkite Culverins.

Karacnos Mortar Battery60″54Heavy 3, Barrage, Blast 3″, Fleshbane, Rad-phage, Ignores Cover, Pinning
Volkite Culverin45″65Heavy 4, Deflagrate

Firing 3, Strength 5, Blast 3″ templates without needing line of sight due to barrage at BS5 is nothing to sniff at; but wounding infantry on 2s and reducing their toughness by 1 when successfully wounded and ignoring cover is outright vicious. Trouble with a 20-man Tactical Squad or a Legion Heavy Support Squad in a building? Karacnos Mortars will deal with them. Pinning doesn’t always help, especially against enemies such as the Death Guard, but it can be useful in some situations. Should any enemies get close or fall into the range of the two forward facing Volkite Culverins, they’ll be faced by up to 8 shots of Volkite burning through them, leaching into others with Deflagrate. This outfit also does go quite the distance at negating the requirement for heavy support to protect against infiltrators or deep striking infantry. Don’t expect the world to turn into a radioactive wasteland or leave burning bodies all over the tabletop, deleting entire squads – though the capability is there in the secondaries alone – this is a more nuanced way of warfare, again forcing an enemy to consider how to deploy against it to minimise the effects.

Platform Modifications:

Occular Augmetics (10pts): This upgrade grants the Night Vision special rule and allows the Knight to re-roll results of 1 on the vehicle damage table when they’re shooting at 12″ or less. This really works at its best on the Porphyrion due to the way its weapons operate over the Asterius calibration brackets – Str 10 AP 3 isn’t setting the world alight. However, the Night Vison rule on the Asterius seriously helps when fighting against Night Lords or in a mission where Night Fighting is in effect by negating the cover save brought in by Night Fighting. It’s a personal decision and based entirely on your opponent, table and chassis in use in my opinion.

Showing off the Karacnos Mortar Battery in the firing position.


A beautiful, complex model which definitely stands out as a centrepiece, the Asterius isn’t the most efficient Acastus Knight; That accolade will always go to the Porphyrion. Offensively however, there’s almost nothing else aside from the Mechanicum Ordinatus Ulator or Titans that provide a genuine full-table threat like the Acastus-class. The former through its unique weapon profile, the latter through overwhelming weapons and manoeuvre capability.

The white elephant in the room in itself is the Warhound Scout Titan at 750pts. This isn’t an issue isolated to the Asterius; both Acastus Class are very close to it in points. This means there’s a very real fight for it to be in game; as a Warhound Titan is genuinely a level above what the Acastus Knights can provide in both offense and defence. Legio Cybernetica and Ordo Reductor armies can both eat into their points very quickly; and only slightly quicker than a Taghmata army can. This means you might be better off taking the Asterius and making the rest of your army more capable and tactically resilient by adding more Thallax or Adsecularis Tech Thralls for those extra 210 points.

The Asterius, though often viewed by heresy players as a bit of a ginger step child compared to the Porphyrion, is still a very capable platform. It’s certainly a little more multi-role than the Porphyrion and it does require some extra thought applied to get the best out of it. Just remember to use that movement to maintain that calibration sweet spot and direct your ion shield towards the greatest threat.

The Asterius is, as a result, the more fun to use of the Acastus Class Knights; the more rewarding to use tactically; and the least likely to earn you the ire of your opponent. It still has the capacity to absolute nuke enemy forces from the table; but it isn’t oppressive as a Porphyrion can be.

A shot of the Dark Mechanicum repaint iinto Xana II and Malinax colours – a long term project that’s taken over a year so far (and this isn’t even half of the army). You can really see how weighty and tall the Acastus Class is.

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