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Nether Fortress

Nether Fortress

A Nether fortress is an uncommon large structure made of Nether bricks found in the Nether, consisting of bridges, corridors, and towers. Nether…

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Generated structures The Nether
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Contents (26)
  1. Generation
  2. Structure
  3. Bounding boxes
  4. Mobs
  5. Java Edition
  6. Bedrock Edition
  7. Loot
  8. Data values
  9. ID
  10. Config
  11. Advancements
  12. Videos
  13. History
  14. Teaser
  15. Java Edition
  16. Bedrock Edition
  17. Legacy Console Edition
  18. New Nintendo 3DS Edition
  19. Issues
  20. Trivia
  21. Gallery
  22. Screenshots
  23. Mojang screenshots
  24. Historical screenshots
  25. In other media
  26. References
"Fortress" redirects here. For other uses, see Fortress (disambiguation).

A Nether fortress is an uncommon large structure made of Nether bricks found in the Nether, consisting of bridges, corridors, and towers. Nether fortresses are the only place where wither skeletons and blazes spawn. They also contain Nether wart.

Generation

Nether fortresses generate in all Nether biomes. To do so, the game splits the Nether into regions in which one of either a fortress or a bastion remnant can generate. The regions are 432×432 blocks in Java Edition and 480×480 blocks in Bedrock Edition.

The Nether structure generation in Java Edition. The black lines represent each region and the dots represent coordinates. The green color is where they can generate and red is where they cannot.

Each region has a four chunk separation located on the south and east borders of the region in which neither a fortress nor a bastion can generate.

The Nether structure generation in Bedrock Edition. The black lines represent each region and the dots represent coordinates. The green color is where they can generate and red is where they cannot.

This leaves only a 368×368 block section in Java Edition or 416×416 block section in Bedrock Edition where a structure can generate.

Two structures never generate in the same region, although they might overlap if they generate close to the separation border. The chance of a fortress attempting to generate instead of a bastion is 2⁄5 (40%) in Java Edition and 1⁄3 (33.3%) in Bedrock Edition. However, if a bastion attempts to generate in the basalt deltas, a fortress generates instead, resulting in fortresses being the most common in the basalt deltas.

Nether fortresses can generate buried in netherrack. In such a case, the interior is not filled with netherrack; all hallways and passages are clear except for open walkways and bridges. It is possible but rare for glowstone or crimson and warped huge fungi to generate inside the fortress pathways.

Structure

Main article: /Structure

Nether fortresses are large complexes composed of Nether bricks supported by pillars that tower high above the lava seas.

Segments of a Nether fortress that are fully enclosed.

The fortress generation starts with a plain four-way crossing centered at chunk coordinates 11, ~, 11 of the designated chunk.

A crossroad found where walkways intersect.

A fortress has two areas, an exterior area of open bridges and an interior area of enclosed corridors. Both the bridges and corridors can end in an unfinished passageway structure or may simply end without elaboration. Fortresses can tunnel through netherrack, giving the "exterior" areas an appearance of tunnels with Nether brick floor and netherrack walls and ceilings. At broken sections the terrain is not cleared, which may create a tunnel that leads straight into a wall of netherrack.

The general pattern of the walkways.
A lava well found inside a Nether fortress.

The exterior consists of:

  • Straight bridges.
  • Up to five plain four-way crossings.
  • Up to four four-way crossings with arches made of Nether brick and Nether brick fences.
  • Up to four small rooms with a single entrance and full-block "stairs" leading to the roof, which may have a single path leading out.
  • Up to 2 blaze monster spawner platforms: structures consisting of three full-block "stairs" leading to a small platform fenced with Nether brick fence, with a blaze monster spawner in the center.
Stairs in a Nether fortress, with Nether wart growing next to them.

The interior of the structures have 1×2 windows with Nether brick fences as the windowpanes. The fences also form gate-like structures at the entrances of some rooms and corridors. Rooms include:

  • The lava well room, which is the connection between the interior and exterior areas.
  • Straight corridors.
  • Up to five four-way crossings.
  • Up to 20 corridor turns (10 right-turns and 10 left-turns), each with a 1⁄3 chance of having a loot chest in the corner.
  • Up to three stairways made from actual stair blocks, leading downward.
  • Up to two three-way intersections with a small exterior balcony.
  • Up to two stairways leading up to a garden of soul sand and Nether wart at the base of the stairs, a corridor leading away from the upper landing and a corridor behind the stairs. If the room is generated embedded in netherrack, only one block above the landing is cleared, with a further indent finishing above the stairs.
An outline of the "bounding boxes".

Bounding boxes

The structure bounding box for the 4-way intersection is pictured above (top-down view), and consists of a 19×11×19 volume centered on the floor block in the center of the intersection. This contrasts many of the other structure bounding boxes as their outlines tend to tightly follow the physical bounds of the structure. Notably, this also means that the fortress supports, which generate outside of that volume and go down to the ground and often into the lava ocean, are not considered part of the fortress for spawning purposes.

The area bounding box is a rectangular box that covers the entire fortress (again, excluding the supports). This is simply the smallest rectangular bounding box that can hold the bounding boxes of all structure pieces in the fortress.

Mobs

Fortresses use a list of possible mobs to spawn that is separate from the rest of the Nether, regardless of the biome the fortress generates in. This includes zombified piglins, skeletons, and magma cubes, as well as two exclusive mobs not found anywhere else: blazes and wither skeletons.

A blaze monster spawner generated in the Nether fortress.

Mobs spawn at a much higher rate if the fortress is surrounded by soul sand valley or warped forest biomes, as hostile mobs in these biomes spawn much less frequently, allowing more hostile mobs to spawn in the fortress‌[JE only][1].

Java Edition

In Java Edition, the spawning algorithm has two checks:

  1. It checks if the spawn coordinates are within the "bounding box" of a single piece (e.g. corridor or walkway) of the fortress. (referred as "structure bounding box" above) In this case the block type of the ground does not matter.
  2. It checks if the spawn coordinates are within the "bounding box" (referred as "area bounding box" above) of the entire fortress and whether the ground consists of Nether bricks (not Nether brick slabs).

If either check passes, it uses the special mob list for fortresses rather than the list for the biome when choosing the mob to spawn. The actual mob spawning proceeds as normal for the mob chosen from this list.

In Java Edition
MobSpawn weightGroup size
Monster category
Blaze10⁄282–3
Wither Skeleton8⁄285
Zombified Piglin5⁄284
Magma Cube3⁄284
Skeleton2⁄285

Bedrock Edition

In Bedrock Edition, instead of spawning anywhere within a structural bounding box, most mobs spawn only in structure spawn locations along varied-length lines spaced apart 4-11 blocks throughout the fortress. They are not set to a particular Y level other than "inside the structure" and are indeed columns several blocks high. They do not require any special type of block, any regular spawnable block suffices.

To identify these spawning columns, glass panes or iron bars can be placed all over the fortress, 1 block above surface blocks. This keeps the mobs stationary. (This technique works in Bedrock because structure spawns occur in the northwest corner of blocks.) Note that these spots may be on top of the raised side blocks, so these side blocks have to be removed before a glass pane grid can be placed.

In Bedrock Edition
MobSpawn weightGroup size
Monster category
Blaze101–2
Wither Skeleton82–3
Zombified Piglin51
Magma Cube32–3
Skeleton22–3

Loot

See also: Chest loot
A chest that generated in a Nether fortress.

Fortresses generate Nether fortress loot with chests in the indoor sections placed at some corridor turns.

In Java Edition and Bedrock Edition, each nether fortress chest contains items drawn from 2 pools, with the following distribution:

Item Stack Size Weight Chance Avg.
per chest
Avg. # chests
to search
2–4× 1× 2–4× 1×
BlockSprite air.png: Sprite image for air in MinecraftNothing[A] —1—14⁄1593.3%0.9331.1
Gold Ingot 1–3—15⁄78—46.5%1.1542.2
Saddle 1—10⁄78—33.3%0.3853.0
Golden Horse Armor 1—8⁄78—27.4%0.3083.6
Nether Wart 3–7—5⁄78—17.9%0.9625.6
Iron Ingot 1–5—5⁄78—17.9%0.5775.6
Diamond 1–3—5⁄78—17.9%0.3855.6
Copper Horse Armor 1—5⁄78—17.9%0.1925.6
Flint and Steel 1—5⁄78—17.9%0.1925.6
Iron Horse Armor 1—5⁄78—17.9%0.1925.6
Golden Sword 1—5⁄78—17.9%0.1925.6
Golden Chestplate 1—5⁄78—17.9%0.1925.6
Diamond Horse Armor 1—3⁄78—11.1%0.1159.0
Obsidian 2–4—2⁄78—7.5%0.23113.4
Rib Armor Trim —1—1⁄156.7%0.06715.0
  1. ↑ 'Nothing' does not refer to the chance of an empty chest. Instead, it refers to the chance that the random loot generator does not add any loot on a single roll.

Data values

ID

Java Edition:

Structure typeIdentifier
EnvSprite nether-fortress.png: Sprite image for nether-fortress in Minecraft Nether Fortressfortress
StructureIdentifier
EnvSprite nether-fortress.png: Sprite image for nether-fortress in Minecraft Nether Fortressfortress

Bedrock Edition:

StructureIdentifier Translation key
EnvSprite nether-fortress.png: Sprite image for nether-fortress in Minecraft Nether Fortressfortress feature.fortress

Config

Java Edition:

  • [NBT Compound / JSON Object] Structure configuration
    • [String] type: minecraft:fortress
    • Fields common to all structures see Template:Nbt inherit/structure/template

Advancements

IconAdvancementIn-game descriptionActual requirements (if different)
A Terrible FortressBreak your way into a Nether FortressEnter a nether fortress.

Videos

History

Teaser

September 16, 2011 Jeb tweets a teaser screenshot of changes to the Nether terrain generation, including fortresses.
September 19, 2011 Jeb releases a second teaser screenshot, showcasing the structure of the then upcoming fortresses.
September 21, 2011 Jeb mentions that he is finished with most of the new Nether features, including two new mobs, one of which is a "retexturing attempt".

Java Edition

Java Edition
1.0.0Beta 1.9 Prerelease Added Nether fortresses.
1.4.212w36a Wither skeletons and skeletons now naturally spawn in fortresses.
As a result, other mobs also found in fortresses spawn less often. Zombie pigmen's spawning weight is halved, making them significantly less common.
1.6.113w18a Chests now generate in fortresses.
1.814w27a Fortresses are now affected by the "Generated structures" option.
14w30a Added possibility of obsidian in chests.
1.915w43a Reduced loot in chests from 2–5 stacks to 2–4 stacks.
1.1620w06a Fortresses can now spawn in the soul sand valley biome.
20w15a Fortresses can now spawn in the basalt deltas biome.
20w16a Fortresses now generate evenly throughout the Nether.
Pre-release 3 Fortresses are now slightly more common.
1.18.2Pre-release 1 If a bastion remnant attempts to generate in a basalt delta, a fortress generates in its place, instead of being skipped entirely.
1.19.4
Experiment
Update 1.20
23w04a Rib armor trim is now found in fortress chests.
23w05a Increased the chance that rib armor trim is found in fortress chests from 4.7% to 6.7%.
1.21.925w31a Copper horse armor is now found in fortress chests.

Bedrock Edition

Pocket Edition Alpha
v0.12.1build 1 Added fortresses.
v0.15.0build 1 Horse armor can now be found in chest loot.
Bedrock Edition
1.19.80
Experiment
Next Major Update
Preview 1.19.80.21 Rib armor trim is now found in fortress chests.
1.20.0Preview 1.20.0.21 Rib armor trims are now available outside the "Next Major Update" experiment.

Legacy Console Edition

Legacy Console Edition
Xbox 360Xbox OnePS3PS4PS VitaWii USwitch
TU7CU11.001.001.00Patch 11.0.1 Added fortresses.
TU9 Changed fortresses to make Nether wart rooms more likely.
TU19CU71.121.121.12 Wither skeletons and skeletons now naturally spawn in fortresses.
As a result, other mobs also found in fortresses spawn less often. Zombie pigmen's spawning weight is halved, making them significantly less common.
Chests now generate.
TU31CU191.221.221.22Patch 3 Added possibility of obsidian in chests.

New Nintendo 3DS Edition

Issues

Issues relating to "Nether Fortress" are maintained on the bug tracker. Issues should be reported and viewed there.

Trivia

  • In rare cases, a fortress may not generate any indoor rooms except one single lava room[2]. This usually occurs when a portion of the exterior section of the fortress blocks the exit to the interior section of the lava well room.
  • Sometimes, two or more fortresses can generate close to or even within one another, creating an even larger cumulative fortress.
  • There is an opening out of the fortress under the lava well, with a single block of Nether bricks from which the lava spreads out.
  • The soul sand valley bone blocks and basalt pillars (down to within three blocks as-usual of a walkway) can replace more Nether bricks. Less-often, huge fungi, Nether wart blocks, warped wart blocks, crimson stems, and warped stems can replace Nether brick, most visibly along walls.
  • A fortress can be seen in the background in the Nether in A Minecraft Movie.[3]

Screenshots

Mojang screenshots

Historical screenshots

In other media

References

  1. ↑ MC-182170 – Mobs spawn at a much higher than normal rate in Nether fortresses, especially in soul sand valleys
  2. ↑ MC-194769 – Nether Fortresses can generate without a lava room and corridor section.
  3. ↑ "We didn’t really go into the Nether Fortress , you just see it in the background: there were some designs made way back but not in the same style as the mobs , probably won’t share that! I agree! They’re awesome once you figure out how not to get hit with their fireballs" – @torfi_F_Olafss on X (formerly Twitter), April 6, 2025
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What spawns in Nether Fortress?
The mob spawn table of this biome with spawn weights and group sizes.
Mob spawns Wiki home