Nether Fortress

Nether Fortress
Biomes	Any Nether biome
Mobs	Blaze; Magma Cube; Skeleton; Wither Skeleton; Zombified Piglin
Consists of	See § Structure; See § Blocks;

There is a related tutorial page for this topic!

See Tutorial:Defeating a Nether fortress.

A Nether fortress is a large structure 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.

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.

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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.

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.

Blocks

Block
Nether Bricks
Nether Brick Fence
Nether Brick Stairs
Soul Sand
Nether Wart
Chest
Blaze Monster Spawner
Lava

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^[1].

Java Edition

In Java Edition, the spawning algorithm has two checks:

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.
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**
Mob	Spawn weight	Group size
Monster category
Blaze	¹⁰⁄₂₈	2–3
Wither Skeleton	⁸⁄₂₈	5
Zombified Piglin	⁵⁄₂₈	4
Magma Cube	³⁄₂₈	4
Skeleton	²⁄₂₈	5

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 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**
Mob	Spawn weight	Group size
Monster category
Blaze	¹⁰⁄₂₈	1–2
Wither Skeleton	⁸⁄₂₈	2–3
Zombified Piglin	⁵⁄₂₈	1
Magma Cube	³⁄₂₈	2–3
Skeleton	²⁄₂₈	2–3

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 ^[A]		Weight ^[B]		Chance ^[C]	Avg. per chest ^[D]	Avg. # chests to search ^[E]
Item	2–4×	1×	2–4×	1×	Chance ^[C]	Avg. per chest ^[D]	Avg. # chests to search ^[E]
Nothing^[F]	—	1	—	¹⁴⁄₁₅	93.3%	0.933	1.1
Gold Ingot	1–3	—	¹⁵⁄₇₃	—	49.0%	1.233	2.0
Saddle	1	—	¹⁰⁄₇₃	—	35.3%	0.411	2.8
Golden Horse Armor	1	—	⁸⁄₇₃	—	29.1%	0.329	3.4
Nether Wart	3–7	—	⁵⁄₇₃	—	19.0%	1.027	5.3
Iron Ingot	1–5	—	⁵⁄₇₃	—	19.0%	0.616	5.3
Diamond	1–3	—	⁵⁄₇₃	—	19.0%	0.411	5.3
Flint and Steel	1	—	⁵⁄₇₃	—	19.0%	0.205	5.3
Iron Horse Armor	1	—	⁵⁄₇₃	—	19.0%	0.205	5.3
Golden Sword	1	—	⁵⁄₇₃	—	19.0%	0.205	5.3
Golden Chestplate	1	—	⁵⁄₇₃	—	19.0%	0.205	5.3
Diamond Horse Armor	1	—	³⁄₇₃	—	11.8%	0.123	8.5
Obsidian	2–4	—	²⁄₇₃	—	8.0%	0.247	12.5
Rib Armor Trim Smithing Template	—	1	—	¹⁄₁₅	6.7%	0.067	15.0

↑ The size of stacks (or for unstackable items, number) of this item on any given roll.
↑ The weight of this item relative to other items in the pool.
↑ The odds of finding any of this item in a single chest.
↑ The number of items expected per chest, averaged over a large number of chests.
↑ The average number of chests the player should expect to search to find any of this item.
↑ '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 type	Identifier
Nether Fortress	`fortress`

Structure	Identifier
Nether Fortress	`fortress`

Bedrock Edition:

Structure	Identifier	Translation key
Nether Fortress	`fortress`	`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

Icon	Advancement	In-game description	Actual requirements (if different)
	A Terrible Fortress	Break your way into a Nether Fortress	Enter a nether fortress.

Video

History

Java Edition
1.0.0			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".
			Beta 1.9 Prerelease				Added Nether fortresses.
1.4.2			12w36a				Wither skeletons and skeletons now naturally spawn in fortresses.
1.4.2			12w36a				As a result, other mobs also found in fortresses spawn less often. Zombie pigmen's spawning weight is halved, making them significantly less common.
1.6.1			13w18a				Chests now generate in fortresses.
1.8			14w27a				Fortresses are now affected by the "Generated structures" option.
1.8			14w30a				Added possibility of obsidian in chests.
1.9			15w43a				Reduced loot in chests from 2–5 stacks to 2–4 stacks.
1.16			20w06a				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			?				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.
1.19.4 Experiment Update 1.20			23w05a				Increased the chance that rib armor trim is found in fortress chests from 4.7% to 6.7%.
Pocket Edition Alpha
v0.12.1			build 1				Added fortresses.
v0.15.0			build 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.
Legacy Console Edition
Xbox 360	Xbox One	PS3	PS4	PS Vita	Wii U	Switch
TU7	CU1	1.00	1.00	1.00	Patch 1	1.0.1	Added fortresses.
TU9	CU1	1.00	1.00	1.00			Changed fortresses to make Nether wart rooms more likely.
TU19	CU7	1.12	1.12	1.12			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.
TU31	CU19	1.22	1.22	1.22	Patch 3		Added possibility of obsidian in chests.
New Nintendo 3DS Edition
0.1.0							Added fortresses.

The first screenshot of Nether fortress.
A brightened version of the previous screenshot.
The second screenshot, showing a large complex of the Nether fortress.
The second screenshot brightened.
A Nether fortress in the overworld.

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]

Gallery

Screenshots

Some Nether warts found at a stair.
A demonstration of the pathway architecture and its ability to cut through netherrack.
The blaze monster spawner room.
The abrupt end of an inside corridor.
The broken passways.
A large amount of corridors. Notice how corridors do not develop arches in their supports.
A ghast that has spawned inside of one of the larger rooms.
A player in a fortress with another Nether fortress across from it.
A fortress with another one generated on top of it.
The lava well room.
A fortress in a warped forest biome.
A fortress in a crimson forest biome.
A fortress in a basalt deltas biome.
A large Nether fortress.
A blaze on fire, preparing to attack.
A flying blaze ready to attack.
A blaze and a wither skeleton in a fortress.
A blaze and a wither skeleton next to a blaze monster spawner.
A blaze monster spawner room surrounded by netherrack.
Ari spying on a fortress using a spyglass.