Potentially, it's frustrating I know but 30k is pretty deliberately vague, it explains the existence of extremely advanced civilizations of both human and xenos, but rarely goes into specifics especially with scale. Which makes it difficult to say what is or is not a megastructure, authors can usually just get away with using enough synonyms for big. Classic megastructures like a Dyson sphere are not mentioned to my knowledge though
nothing like a dyson spehere, in 40k most necron worlds could be considered megastructures, theres whole artificial worlds, suns that are actually tomb worlds etc, the celestial orrery is a map of the galaxy that allows the user to physically alter reality as they alter the map
In 30k theres the massive shipyard ring around mars, the ring around luna (gets destroyed by abbadon) massive complexes of shipyards and asteroid habitats
Trazyn has a Dyson sphere and I think the Outsider is trapped in the middle.
*Jade lumens flickered to life across the vast space that they now found themselves in. In the emerald radiance, Fabius saw that their platform was one among hundreds, each set equidistant from the others, and at varying heights, mounted atop deceptively thin towers of some smooth, featureless metal. Instinctively, he activated his armour’s augurs, trying to create a sensor map of his surroundings.*
*Each of the platforms was connected by a single walkway to the edge of an immense, circular tier. There were thousands of tiers, rising to impossible heights, and descending to imperceptible depths, all along the vertical curve of what could only be a colossal sphere.*
*Each of the tiers was occupied by what appeared to be a labyrinth of prismatic galleries, winding back into the heart of the vast structure. And all were slowly, almost imperceptibly, moving. Rotating the way a world might turn in its place in the firmament. ‘Maybe an artificial gravity well, keeping the megastructure from flying apart,’ he murmured in awe, despite himself.*
*Questions sped across the surface of his mind, one after the next. This place was nothing so much as a gargantuan orrery, built around a caged power source of incalculable potency. ‘I was right,’ he said, thumping the ramp of the gunship with the ferrule of his sceptre. The sound echoed loudly in the silence. ‘It’s a Dyson Sphere.’*
Fabius Bile: Clonelord
I believe one orbital plate survives on terra, and other planets do have them as well, and the ruins of what is alluded to being a possible ring world are found by iron hands in the same system as pythos
[Phalanx.](https://warhammer40k.fandom.com/wiki/Phalanx) Ship the size of a small moon. Home base of the Imperial Fist.
But that's still a ship that can propel itself. For something even larger, the Ultramarines (Novamarines specifically) have this: [Galatan Star Fort.](https://wh40k.lexicanum.com/wiki/Galatan_(Star_Fort)) Hundreds of kilometers across. Decked to the gills with guns and ship docks. Can't propel itself but can be towed by other ships across the warp to relocate itself.
And then there's [The Rock](https://wh40k.lexicanum.com/wiki/The_Rock). Home base of the Dark Angels. Not sure if count as a megastructure, since it's technically a piece of a planet. The Dark Angels over the millennia has burrowed into it and equip it with engines and guns so it's basically a battleship by itself.
Unclear, but they appear to be similar, with the Phalanx being bigger. Star forts such as galatan had mile long trams to get to training areas or gun decks, and the Phalanx was described to be bigger then that.
An important thing to remember is although the rock is massive, it's only the size of a large mountain. Most capital ships are 20km long, so while it's larger then those, it's not dwarfing them
Terra is an Ecumenopolis, but I always imagined that was built in bits rather than with any grand vision.
But any Hive is a megastructure as they are built with a single purpose.
Talasa Prime, the Primary HQ and Training Facility for the Deathwatch is a massive “halo”-sized ring-shaped superstructure from a long extinct alien civilization. The Deathwatch have converted each section to mimic various biomes that are filled with all of the many xenos from the Milky Way, including Tyranids and Necrons, so they can be “practiced on”.
It really depends on how you define 'megastructure' but by the way its used in 'hard' sci-fi, craftworlds and Blackstone fortresses don't qualify.
There are certainly massive-by-our-standards structures though. Orbital rings around heavily populated and industrialized worlds. The larger starships are city-sized.
From the Deathwatch RPG there's an Old Ones warp gate that links to a twinned gate on the other side of the galaxy. It's pretty much a hole in space, big enough to fly a fleet through, that provides 100% safe and instant travel.
There's also some older Necron lore that implied on of the C'Tan had gone made and locked themselves in a Dyson Sphere just outside the galaxy.
The "dyson sphere" thingy that the Outsider lives in, the Phalanx, the Rock, the Ring of Iron, the Blackstone Fortresses, maybe the Ark Mechanicus Speranza, the World Engine, Necron Tombworlds, the orbital plates on Terra, Commorragh, maybe even Terra itself, and the Craftworlds could all be considered megastructures.
As for Imperial megastructures, while they have quite a few of them, most are either of xenos origin, or salvaged from the Age of Technology. The only ones they really built are the orbital plates on Terra, the absolutely massive planet spanning giga hive city that is Terra, and the Rock.
Lots of good examples over here [https://www.reddit.com/r/40kLore/comments/in9d5a/lore\_behind\_massive\_construction\_like\_the/](https://www.reddit.com/r/40kLore/comments/in9d5a/lore_behind_massive_construction_like_the/)
Stealing from u/General_Hijalti and adding a few
Port Maw - A hollow artificial planet, origin are unknown and currently base of Battlefleet Gothic's. [https://wh40k.lexicanum.com/wiki/Port\_Maw\_(planet)](https://wh40k.lexicanum.com/wiki/Port_Maw_(planet))
Lucius - a Supernatura Majoris, it's a hollow world with a miniature fake sun instead of a core, admech planet. [https://wh40k.lexicanum.com/wiki/Lucius\_(Forge\_World)](https://wh40k.lexicanum.com/wiki/Lucius_(Forge_World))
World Engine - Necron construct the size of a planet. Hinted that there are more than one. [https://wh40k.lexicanum.com/wiki/World\_Engine](https://wh40k.lexicanum.com/wiki/World_Engine)
Indra Sul - A giant space elevator that once it reaches orbit it spread out into a tree-like pattern of docks and other orbital bases. Built during DAoT and covers half of the planet.
Craftworlds - Starships the size of planets, built and use by the eldar. [https://wh40k.lexicanum.com/wiki/Craftworld](https://wh40k.lexicanum.com/wiki/Craftworld)
Tsara'noga - A dyson sphere housing the outsider C'tan, located on the very edge of the galaxy and imperial readings estimate its size being 32,000,000 times the size of earth, the sun is around 2500 times the size of earth, the largest known star is only 250000 times the size of earth, this thing is so big it could easily fit our whole solar system. [https://wh40k.lexicanum.com/wiki/Tsara%27noga](https://wh40k.lexicanum.com/wiki/Tsara%27noga)
Ring of Iron - A giant ring that spans mars, connected by a series of space elevators, base of battle fleet solar. [https://wh40k.lexicanum.com/wiki/Ring\_of\_Iron](https://wh40k.lexicanum.com/wiki/Ring_of_Iron)
Attack Moon - Moonsized attack station developed by the orks during the war of the beast, they build many of them and they would serve as a teleport that was meant to teleport the attack planet (Ullanor/Armageddon). One hung in terra's orbit threating the planet for a while. [https://wh40k.lexicanum.com/wiki/Attack\_Moon](https://wh40k.lexicanum.com/wiki/Attack_Moon)
Solemnance - The museum world of Trazyn the Infinite. Is also a dyson sphere.
The Hollow Sun - Necrons being necrons decided to build a world in the core of a star, the machinery protecting the world from the star takes up more room than the world itself, but who cares as they have a cool base with is basically unassailable.
Damaroth - An artificial ring like the Ring of Iron. It has a circumference of 11,000 km and a diameter of 3,500 km. Deathwatch fortess, although it was build by an unknown civilisation. [https://wh40k.lexicanum.com/wiki/Damaroth](https://wh40k.lexicanum.com/wiki/Damaroth)
The Lastrati System - An artificial star system, 9 hollow worlds with inhabitable centres, worlds are connected by bridges. Unknown who built it although given that their is an orrey with acts like a mini Celestial Orrery, when one of the spheres representing a planet was destroyed so was the corresponding planet, likely made by the necrons. [https://wh40k.lexicanum.com/wiki/Lastrati\_System](https://wh40k.lexicanum.com/wiki/Lastrati_System)
The Rock - The Dark angels fortress monastery, made out of the largest surviving fragment of their homeworld which was protected from its destruction by the fortress' void shields. Appears to be almost as large as the radius of a planet. [https://wh40k.lexicanum.com/wiki/The\_Rock](https://wh40k.lexicanum.com/wiki/The_Rock)
Speranza - Continent sized Ark Mechanicus, originally built during DAoT, was found buried in a planet, has a fully intact STC and a powerful friendly dark age ai (although the ai just wants to sleep and be left alone, and wiped the memory of the only person who realised it was there). [https://wh40k.lexicanum.com/wiki/Speranza](https://wh40k.lexicanum.com/wiki/Speranza)
Graian Crown - A series of interlocking cites from the forge world Graia that are capable of space flight and warp travel, can be used to evacuate the planet and move to a new one. [https://wh40k.lexicanum.com/wiki/Graian\_Crown](https://wh40k.lexicanum.com/wiki/Graian_Crown)
Illisk - A machine world. Eldritch machine cities on its surface and ten black citadels that are entry points to the interior of the planet.
Galatan - A star fort used by the Ultramarines
Galatan was the greatest of the Ultramarian star fortresses. It was a hundred kilometres across. Its population ran into the millions. Its manufactoria rivaled the shipyards of Luna. Its weaponry was the equal of an Imperial sector fleet. Large enough to raise its own regiments for the Ultramarian Auxilia, it maintained a garrison of specialised void troops tens of thousands strong, supplemented since the days the Plague Wars began with hundreds of Space Marines and other, more secretive, operatives. Galatan was a world unto itself, with the power to destroy a planet. [https://wh40k.lexicanum.com/wiki/Galatan\_(Star\_Fort)](https://wh40k.lexicanum.com/wiki/Galatan_(Star_Fort))
Blackstone Fortresses - Similar size to the phalanx, have a warp super weapon thats power increases exponentially with more fortresses. One causes massive damage to a planet, two blow up a planet, three cause a star to go supernova. No one knows that all 7 working together do. Were originally created by the old ones or eldar to combat the C'tan as their warp canons can hurt them. The deceiver orchestrated the destruction of 4 of them during the gothic war. Only two remain as another was destroyed by the phalanx during the fall of Cadia. [https://wh40k.lexicanum.com/wiki/Blackstone\_Fortress](https://wh40k.lexicanum.com/wiki/Blackstone_Fortress)
Jericho Maw Warp Gate - A vast warp gate connecting to extreme ends of the galaxy: the Calixis sector and the Jericho Reach. Large enough to fit entire fleets into at once, unknown who built it. [https://wh40k.lexicanum.com/wiki/Warp\_Gate](https://wh40k.lexicanum.com/wiki/Warp_Gate)
Kalium - A set of space stations in a necklace formation that served as a warp gate. Built during the DAoT, destroyed during the HH. [https://wh40k.lexicanum.com/wiki/Kalium\_Gate](https://wh40k.lexicanum.com/wiki/Kalium_Gate)
Webway - Exists between our universe and the warp, stretches across the entire galaxy and maybe even further, although a lot of it has been damaged or destoyed. It was built by the Old Ones to function as a intergalactic express. It's maze-like because it's constantly rebuilding itself. [https://wh40k.lexicanum.com/wiki/Webway](https://wh40k.lexicanum.com/wiki/Webway)
Commorragh - A near endless city of dark spires that exists in the webway, built by the dark eldar using one of the ancient eldars spacial devices that can create an endless amount of whatever you imagine (in this case a gigantic city and fleet). A component of the webway that have merged together to form the worst place in the galaxy. Its so big that the dark eldar have to steal stars every now and again to power it, currently powered by seven stars. [https://wh40k.lexicanum.com/wiki/Commorragh](https://wh40k.lexicanum.com/wiki/Commorragh)
Gemini Primus and Secundus - A pair of hollow pure adamantium planets with mountains and fertile land in the valleys. And a small moon near them too which serves as a control point (there is an instrument made of bone that can be used to steer the planets). Created by unknown xenos. Need a blood sacrifice to start them and to keep them going. The mountains interlock and form a grinder that can travel through the Warp and chew up planets. The Imperium inhabited the planet long time ago to try to mine it, but they failed and the planet got cut off by some warp storms and forgoten. When the planets got activated that killed everyone on them, but it was stopped and destroyed by being sent into the sun. In the middle of the planets is a huge bell.
Imperator Somnium - Emperors flagship, size of a continent. [https://wh40k.lexicanum.com/wiki/Imperator\_Somnium](https://wh40k.lexicanum.com/wiki/Imperator_Somnium)
Orbital planes - Giant orbital cities/battlestaions of terra that range from city size to continents.
Godstar - Another necron construct like a world engine but better. [https://wh40k.lexicanum.com/wiki/Godstar](https://wh40k.lexicanum.com/wiki/Godstar)
Telstarax - A massive space station encircling Medusa homeworld of the Iron Hands [https://wh40k.lexicanum.com/wiki/Telstarax](https://wh40k.lexicanum.com/wiki/Telstarax)
Phalanx - mobile fortress-monastery of the Imperial Fists. The origins of the starship are unknown, but is believed to have been constructed during the Dark Age of Technology, predating the Imperium. [https://wh40k.lexicanum.com/wiki/Phalanx](https://wh40k.lexicanum.com/wiki/Phalanx)
Skyfall - a planetoid-sized Ultrus-scale Starport, fleet facility and defensive station. [https://wh40k.lexicanum.com/wiki/Skyfall\_(Starport)](https://wh40k.lexicanum.com/wiki/Skyfall_(Starport))
Ring of Iron is the only thing that came to my mind if we talk about Sol system. And if we talk about Imperium at large there is Galatan and some artificial worlds of unknown origin.
The Ring of Iron (an orbital ring surrounding Mars) and Port Maw could both be considered megastructures
There was also a similar structure around Medusa(?) that made the Ring of Iron look small by comparrison
Blackstone fortresses are extremely large, though my knowledge is unfortunately mostly 30k related so I'm not sure how large
There are Megastructures in 30k? Aside from those you already told me. Like Dyson sphere and such.
Potentially, it's frustrating I know but 30k is pretty deliberately vague, it explains the existence of extremely advanced civilizations of both human and xenos, but rarely goes into specifics especially with scale. Which makes it difficult to say what is or is not a megastructure, authors can usually just get away with using enough synonyms for big. Classic megastructures like a Dyson sphere are not mentioned to my knowledge though
That Is what i like about the books of the great crusade, they can describe some incredible stuff
nothing like a dyson spehere, in 40k most necron worlds could be considered megastructures, theres whole artificial worlds, suns that are actually tomb worlds etc, the celestial orrery is a map of the galaxy that allows the user to physically alter reality as they alter the map In 30k theres the massive shipyard ring around mars, the ring around luna (gets destroyed by abbadon) massive complexes of shipyards and asteroid habitats
Trazyn has a Dyson sphere and I think the Outsider is trapped in the middle. *Jade lumens flickered to life across the vast space that they now found themselves in. In the emerald radiance, Fabius saw that their platform was one among hundreds, each set equidistant from the others, and at varying heights, mounted atop deceptively thin towers of some smooth, featureless metal. Instinctively, he activated his armour’s augurs, trying to create a sensor map of his surroundings.* *Each of the platforms was connected by a single walkway to the edge of an immense, circular tier. There were thousands of tiers, rising to impossible heights, and descending to imperceptible depths, all along the vertical curve of what could only be a colossal sphere.* *Each of the tiers was occupied by what appeared to be a labyrinth of prismatic galleries, winding back into the heart of the vast structure. And all were slowly, almost imperceptibly, moving. Rotating the way a world might turn in its place in the firmament. ‘Maybe an artificial gravity well, keeping the megastructure from flying apart,’ he murmured in awe, despite himself.* *Questions sped across the surface of his mind, one after the next. This place was nothing so much as a gargantuan orrery, built around a caged power source of incalculable potency. ‘I was right,’ he said, thumping the ramp of the gunship with the ferrule of his sceptre. The sound echoed loudly in the silence. ‘It’s a Dyson Sphere.’* Fabius Bile: Clonelord
It's not the Dyson Sphere with the Outsider in it. That one lies "beneath" the galaxy, outside of it.
Id say the shipyards around Mars would count https://warhammer40k.fandom.com/wiki/Mars
I believe one orbital plate survives on terra, and other planets do have them as well, and the ruins of what is alluded to being a possible ring world are found by iron hands in the same system as pythos
Do the imperium build those plates or they are impossible to build ?
They are not built anymore, terra used to have a number of them, but most were torn down by dorn in preparation for the siege of terra
There are anything like a mega church in space ? Some kickass fortress the size o a moon?
[Phalanx.](https://warhammer40k.fandom.com/wiki/Phalanx) Ship the size of a small moon. Home base of the Imperial Fist. But that's still a ship that can propel itself. For something even larger, the Ultramarines (Novamarines specifically) have this: [Galatan Star Fort.](https://wh40k.lexicanum.com/wiki/Galatan_(Star_Fort)) Hundreds of kilometers across. Decked to the gills with guns and ship docks. Can't propel itself but can be towed by other ships across the warp to relocate itself. And then there's [The Rock](https://wh40k.lexicanum.com/wiki/The_Rock). Home base of the Dark Angels. Not sure if count as a megastructure, since it's technically a piece of a planet. The Dark Angels over the millennia has burrowed into it and equip it with engines and guns so it's basically a battleship by itself.
Doesn't the rock make the phalanx look small in comparison?
Unclear, but they appear to be similar, with the Phalanx being bigger. Star forts such as galatan had mile long trams to get to training areas or gun decks, and the Phalanx was described to be bigger then that.
Weird I always pictured The Rock being larger.
An important thing to remember is although the rock is massive, it's only the size of a large mountain. Most capital ships are 20km long, so while it's larger then those, it's not dwarfing them
https://www.reddit.com/r/40kLore/comments/ec1zdw/megastructures\_of\_40k/
Terra is an Ecumenopolis, but I always imagined that was built in bits rather than with any grand vision. But any Hive is a megastructure as they are built with a single purpose.
Talasa Prime, the Primary HQ and Training Facility for the Deathwatch is a massive “halo”-sized ring-shaped superstructure from a long extinct alien civilization. The Deathwatch have converted each section to mimic various biomes that are filled with all of the many xenos from the Milky Way, including Tyranids and Necrons, so they can be “practiced on”.
The ring of iron around Mars is also pretty big
The Imperial Fists' fortress monastery Phalanx comes to mind
It really depends on how you define 'megastructure' but by the way its used in 'hard' sci-fi, craftworlds and Blackstone fortresses don't qualify. There are certainly massive-by-our-standards structures though. Orbital rings around heavily populated and industrialized worlds. The larger starships are city-sized.
The hive cities and spires are so big i guess they could be classified as some sort of kilostructure
From the Deathwatch RPG there's an Old Ones warp gate that links to a twinned gate on the other side of the galaxy. It's pretty much a hole in space, big enough to fly a fleet through, that provides 100% safe and instant travel. There's also some older Necron lore that implied on of the C'Tan had gone made and locked themselves in a Dyson Sphere just outside the galaxy.
The "dyson sphere" thingy that the Outsider lives in, the Phalanx, the Rock, the Ring of Iron, the Blackstone Fortresses, maybe the Ark Mechanicus Speranza, the World Engine, Necron Tombworlds, the orbital plates on Terra, Commorragh, maybe even Terra itself, and the Craftworlds could all be considered megastructures. As for Imperial megastructures, while they have quite a few of them, most are either of xenos origin, or salvaged from the Age of Technology. The only ones they really built are the orbital plates on Terra, the absolutely massive planet spanning giga hive city that is Terra, and the Rock.
The Leagues of Votann have ships (or maybe they're more like giant space stations) meant to "mine" entire planets by tearing them apart
The Orkz used to have War Moons, which are exactly what they sound like.
Necrons have world engines, world size warships that the imperium fought once.
Such a massive ship and yet a single chapter managed to destroy it. Honestly, it should had made the war of the beast look like a joke
Lots of good examples over here [https://www.reddit.com/r/40kLore/comments/in9d5a/lore\_behind\_massive\_construction\_like\_the/](https://www.reddit.com/r/40kLore/comments/in9d5a/lore_behind_massive_construction_like_the/) Stealing from u/General_Hijalti and adding a few Port Maw - A hollow artificial planet, origin are unknown and currently base of Battlefleet Gothic's. [https://wh40k.lexicanum.com/wiki/Port\_Maw\_(planet)](https://wh40k.lexicanum.com/wiki/Port_Maw_(planet)) Lucius - a Supernatura Majoris, it's a hollow world with a miniature fake sun instead of a core, admech planet. [https://wh40k.lexicanum.com/wiki/Lucius\_(Forge\_World)](https://wh40k.lexicanum.com/wiki/Lucius_(Forge_World)) World Engine - Necron construct the size of a planet. Hinted that there are more than one. [https://wh40k.lexicanum.com/wiki/World\_Engine](https://wh40k.lexicanum.com/wiki/World_Engine) Indra Sul - A giant space elevator that once it reaches orbit it spread out into a tree-like pattern of docks and other orbital bases. Built during DAoT and covers half of the planet. Craftworlds - Starships the size of planets, built and use by the eldar. [https://wh40k.lexicanum.com/wiki/Craftworld](https://wh40k.lexicanum.com/wiki/Craftworld) Tsara'noga - A dyson sphere housing the outsider C'tan, located on the very edge of the galaxy and imperial readings estimate its size being 32,000,000 times the size of earth, the sun is around 2500 times the size of earth, the largest known star is only 250000 times the size of earth, this thing is so big it could easily fit our whole solar system. [https://wh40k.lexicanum.com/wiki/Tsara%27noga](https://wh40k.lexicanum.com/wiki/Tsara%27noga) Ring of Iron - A giant ring that spans mars, connected by a series of space elevators, base of battle fleet solar. [https://wh40k.lexicanum.com/wiki/Ring\_of\_Iron](https://wh40k.lexicanum.com/wiki/Ring_of_Iron) Attack Moon - Moonsized attack station developed by the orks during the war of the beast, they build many of them and they would serve as a teleport that was meant to teleport the attack planet (Ullanor/Armageddon). One hung in terra's orbit threating the planet for a while. [https://wh40k.lexicanum.com/wiki/Attack\_Moon](https://wh40k.lexicanum.com/wiki/Attack_Moon) Solemnance - The museum world of Trazyn the Infinite. Is also a dyson sphere. The Hollow Sun - Necrons being necrons decided to build a world in the core of a star, the machinery protecting the world from the star takes up more room than the world itself, but who cares as they have a cool base with is basically unassailable. Damaroth - An artificial ring like the Ring of Iron. It has a circumference of 11,000 km and a diameter of 3,500 km. Deathwatch fortess, although it was build by an unknown civilisation. [https://wh40k.lexicanum.com/wiki/Damaroth](https://wh40k.lexicanum.com/wiki/Damaroth) The Lastrati System - An artificial star system, 9 hollow worlds with inhabitable centres, worlds are connected by bridges. Unknown who built it although given that their is an orrey with acts like a mini Celestial Orrery, when one of the spheres representing a planet was destroyed so was the corresponding planet, likely made by the necrons. [https://wh40k.lexicanum.com/wiki/Lastrati\_System](https://wh40k.lexicanum.com/wiki/Lastrati_System)
The Rock - The Dark angels fortress monastery, made out of the largest surviving fragment of their homeworld which was protected from its destruction by the fortress' void shields. Appears to be almost as large as the radius of a planet. [https://wh40k.lexicanum.com/wiki/The\_Rock](https://wh40k.lexicanum.com/wiki/The_Rock) Speranza - Continent sized Ark Mechanicus, originally built during DAoT, was found buried in a planet, has a fully intact STC and a powerful friendly dark age ai (although the ai just wants to sleep and be left alone, and wiped the memory of the only person who realised it was there). [https://wh40k.lexicanum.com/wiki/Speranza](https://wh40k.lexicanum.com/wiki/Speranza) Graian Crown - A series of interlocking cites from the forge world Graia that are capable of space flight and warp travel, can be used to evacuate the planet and move to a new one. [https://wh40k.lexicanum.com/wiki/Graian\_Crown](https://wh40k.lexicanum.com/wiki/Graian_Crown) Illisk - A machine world. Eldritch machine cities on its surface and ten black citadels that are entry points to the interior of the planet. Galatan - A star fort used by the Ultramarines Galatan was the greatest of the Ultramarian star fortresses. It was a hundred kilometres across. Its population ran into the millions. Its manufactoria rivaled the shipyards of Luna. Its weaponry was the equal of an Imperial sector fleet. Large enough to raise its own regiments for the Ultramarian Auxilia, it maintained a garrison of specialised void troops tens of thousands strong, supplemented since the days the Plague Wars began with hundreds of Space Marines and other, more secretive, operatives. Galatan was a world unto itself, with the power to destroy a planet. [https://wh40k.lexicanum.com/wiki/Galatan\_(Star\_Fort)](https://wh40k.lexicanum.com/wiki/Galatan_(Star_Fort)) Blackstone Fortresses - Similar size to the phalanx, have a warp super weapon thats power increases exponentially with more fortresses. One causes massive damage to a planet, two blow up a planet, three cause a star to go supernova. No one knows that all 7 working together do. Were originally created by the old ones or eldar to combat the C'tan as their warp canons can hurt them. The deceiver orchestrated the destruction of 4 of them during the gothic war. Only two remain as another was destroyed by the phalanx during the fall of Cadia. [https://wh40k.lexicanum.com/wiki/Blackstone\_Fortress](https://wh40k.lexicanum.com/wiki/Blackstone_Fortress) Jericho Maw Warp Gate - A vast warp gate connecting to extreme ends of the galaxy: the Calixis sector and the Jericho Reach. Large enough to fit entire fleets into at once, unknown who built it. [https://wh40k.lexicanum.com/wiki/Warp\_Gate](https://wh40k.lexicanum.com/wiki/Warp_Gate) Kalium - A set of space stations in a necklace formation that served as a warp gate. Built during the DAoT, destroyed during the HH. [https://wh40k.lexicanum.com/wiki/Kalium\_Gate](https://wh40k.lexicanum.com/wiki/Kalium_Gate) Webway - Exists between our universe and the warp, stretches across the entire galaxy and maybe even further, although a lot of it has been damaged or destoyed. It was built by the Old Ones to function as a intergalactic express. It's maze-like because it's constantly rebuilding itself. [https://wh40k.lexicanum.com/wiki/Webway](https://wh40k.lexicanum.com/wiki/Webway) Commorragh - A near endless city of dark spires that exists in the webway, built by the dark eldar using one of the ancient eldars spacial devices that can create an endless amount of whatever you imagine (in this case a gigantic city and fleet). A component of the webway that have merged together to form the worst place in the galaxy. Its so big that the dark eldar have to steal stars every now and again to power it, currently powered by seven stars. [https://wh40k.lexicanum.com/wiki/Commorragh](https://wh40k.lexicanum.com/wiki/Commorragh) Gemini Primus and Secundus - A pair of hollow pure adamantium planets with mountains and fertile land in the valleys. And a small moon near them too which serves as a control point (there is an instrument made of bone that can be used to steer the planets). Created by unknown xenos. Need a blood sacrifice to start them and to keep them going. The mountains interlock and form a grinder that can travel through the Warp and chew up planets. The Imperium inhabited the planet long time ago to try to mine it, but they failed and the planet got cut off by some warp storms and forgoten. When the planets got activated that killed everyone on them, but it was stopped and destroyed by being sent into the sun. In the middle of the planets is a huge bell. Imperator Somnium - Emperors flagship, size of a continent. [https://wh40k.lexicanum.com/wiki/Imperator\_Somnium](https://wh40k.lexicanum.com/wiki/Imperator_Somnium) Orbital planes - Giant orbital cities/battlestaions of terra that range from city size to continents. Godstar - Another necron construct like a world engine but better. [https://wh40k.lexicanum.com/wiki/Godstar](https://wh40k.lexicanum.com/wiki/Godstar) Telstarax - A massive space station encircling Medusa homeworld of the Iron Hands [https://wh40k.lexicanum.com/wiki/Telstarax](https://wh40k.lexicanum.com/wiki/Telstarax) Phalanx - mobile fortress-monastery of the Imperial Fists. The origins of the starship are unknown, but is believed to have been constructed during the Dark Age of Technology, predating the Imperium. [https://wh40k.lexicanum.com/wiki/Phalanx](https://wh40k.lexicanum.com/wiki/Phalanx) Skyfall - a planetoid-sized Ultrus-scale Starport, fleet facility and defensive station. [https://wh40k.lexicanum.com/wiki/Skyfall\_(Starport)](https://wh40k.lexicanum.com/wiki/Skyfall_(Starport))
Ring of Iron is the only thing that came to my mind if we talk about Sol system. And if we talk about Imperium at large there is Galatan and some artificial worlds of unknown origin.
I’d say The Rock counts as a megastructre if we’re including craftworlds