Minecraft Forums

Quote from Venari

What is a dungeon precisely? What blocks are present? Is it simply just a cave you find while you mine? A Ravine? A dark hole anywhere?

Quote from Tffen

Is there anywhere on the wiki I can read about this? This is completely new to me, as I haven't been playing mc for a long time.

Quote from Kholdstare

Personally, I think the witch is the wood structure.

You see, wood floats and ducks float. If ducks float, ducks are made of wood. If witches burn, they must also be made of wood. If ducks and witches are both made of wood, they both float.

So, toss the wood structure in a lake and see if it floats. If it does, it's a witch.

(video courtesy of qmagnet)

VILLAGE MECHANICS: A NOT-SO-BRIEF GUIDE
by IronMagus

...or "Everything you (n)ever wanted to know about NPC villages, but were afraid to ask." If you're trying to spawn golems for an iron ingot farm, or just want a few more noses to trade with in your local testificate township, then you've come to the right place. Much of what's in here comes from another forum thread originally posted by Marfagames. Among the many others who have helped me piece together this knowledge, special thanks must also go out to forum members trunkz and KyoShinda, both frequent posters in that same thread. Together the three of them made most of this information available in the first place -- all I did was digest what they wrote and re-word it into something that I, and I'm hoping you as well, could understand a little easier. And now, on to the good stuff!

SECTION ZERO: TERMINOLOGY

...or "What is this I don't even." A village is defined by several factors: the village center, radius or "size", number of houses, population (number of villagers), population cap (max. number of villagers, based on housing), number of golems, and golem cap (based on population).

You might be asking yourself, "what does it take to make a village?" In order to be recognized as a "village," two things are required: at least one villager, and at least one house. A "house" is defined simply as a wooden door with an "inside" and an "outside" (see the next section for details.) A village's population is capped at 35% of the number of "houses" (doors.) Under ideal conditions, villagers will breed up to this limit, and then stop. Iron golems can spawn in villages of sufficient size, and the golem cap is 10% of the village's current population.

The village center is the geometric center point, or "average coordinates" of all the doors. The village size or radius is the greater of either 32 blocks, or one plus the distance from this center point to the furthest door (measured in "straight line" or Euclidean distance). This means that the radius is always at least 32, no matter what, but it can be more than that if there are any houses further than 32 blocks from the center. If there are, then the radius is one block larger than the distance to the farthest one.

Both the center point and radius are rounded to whole numbers. The center point is rounded "towards zero" (down if the value is positive, up if the value is negative. Or in other words, it is not "rounded" at all but simply truncated at the decimal point). In preliminary testing, the radius appears to be the raw distance from the rounded center point to the furthest door, plus one, rounded up, although more testing or a look into the game code are required to confirm this.

SECTION 1: HOUSING

...or "You can't park here." How does the game recognize a "house"? A house is defined as a wooden door with an "inside" and an "outside." The inside is the side which has more spaces covered by "roof" blocks than the other, within five spaces horizontally of the door in the two directions it faces. A "roof" block is an opaque block, at any height not lower than the door, that blocks direct sunlight from reaching the spaces below it.

Another way to put it would be to say that an "outside" space has a direct view of the sky, and so has a "SL" (sky light) value of 15. An "inside" space does not have a direct view of the sky (not looking straight up, anyway) and a "SL" value of less than 15. The "inside" is the side which has more "inside spaces" than the "outside" (which, in turn, has more "outside spaces" than the "inside.")

A door is not counted as a house without a "roof," or with the same number of covered spaces on either side.

Example - The door is placed on the wooden planks. The game checks the spaces represented by the light blue wool, to see if they are covered by a "roof" block or not:

Fig. 1

The simplest house looks something like this. Just a wooden door, with a dirt block on the ground next to it:

Fig. 2

Yes that is a valid house! Not much to look at, is it? But it fits the criteria. The dirt blocks the light from reaching the space below it, and so counts as a roof block.

There is one "inside" space, covered by a roof block, on the right side of the image, and zero on the left. Since "one" is more than "zero," there are more covered spaces on one side of the door than there are on the other, and so the game counts this as a house. Here is a cutaway view of the same setup, with colored wool for a visual aid. The red wool is covered by a roof block and considered an "inside" space; the blue blocks are "outside":

Fig. 3

The following are all examples of houses as well:

Figs. 4-7:

Fig. 4


Fig. 5


Fig. 6


Fig. 7

It doesn't matter what you build, except for what's directly above the colored wool. Anything to the sides of this can be whatever you want, or nothing at all:

Fig. 8

The dirt blocks on the far side (top of image) do not affect this house's "housiness," nor do the lack of any blocks on the near side.

A door is two blocks tall, and this check is performed twice per door, if necessary. If the initial "roof check" (see Fig. 1) fails, then the bottom-most layer is ignored and the check is performed a second time, starting one layer higher. This time, only the spaces above the lime-green wool (and not the first layer, here occupied by the wool itself) are checked for roof blocks:

Fig. 9

Example - For the door pictured below, the initial roof check finds there are two spaces covered by roof blocks on the left side, and two covered spaces on the right side as well. With the same number of covered spaces on each side, neither one can be designated the "inside" or the "outside," and so the door is not counted as a house (yet. But but we're not through yet, either.):

Fig. 10

Then since the initial check failed, the bottom layer is ignored, and we perform the test again, this time starting one block higher, checking for roof blocks only above (not level with) the green wool. This time, only the two spaces on the left-hand side of the image are covered. Since the "roof check" passed on this second try, the door counts as a house, and its "inside" is on the left where the more covered spaces are:

Fig. 11

In the next example, the door passes the test on the initial first check. It has one covered space on the left side and two on the right. This makes it a house with the "inside" to the right. The second check would pass as well (with the "inside" on the left this time), but since the first one already passed, we don't even bother testing again. This door counts as a house, with the "inside" on the right:

Fig. 12

"Inside" on the right.

The covered spaces don't have to be contiguous. The door below is a house, with the "inside" on the right, which has three covered spaces, versus only two on the left.:

Fig. 13

"Inside" on the right.

This next door has three covered spaces on each side, and is not a house:

Fig. 14

NOT A HOUSE!!

For a house to be a house, it has to be "seen" by a nearby villager. (I use the word "see" here loosely. This is actually based on proximity, not line-of-sight. A villager doesn't literally have to see the door to recognize it, it's enough just to be within range.) Without a villager nearby to "see" the house and recognize it as such, it is not considered a "house" but just some blocks and a door. The following image utilizes Trunkz' "Village Info" mod which adds info about the nearest village to the F3 display. Note the phrase "No Village Found" in the bottom-left:

Fig. 15

Not technically a house, since there is no villager here.

But as soon as a villager shows up, it becomes a proper village, with a house and everything:

Fig. 16

The "Houses" value in red indicates that there are not enough to support an iron golem. If there were 21 or more it would shift to green indicating that a golem(s) can spawn in the village.

Villagers will recognize a house within sixteen blocks along both horizontal axes, and up to three blocks above or five blocks below the level of the ground the villager is standing on:

Fig. 17

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Combining villages:

When two villages' boundaries overlap, they will merge into a single, larger village. A new house that's within (radius + 32) of an existing village would, were it considered a village in its own right, overlap with the existing village and so just becomes a part of that village. This causes a recalculation of the village's radius and center point, which can sometimes cause it to overlap with another already-existing village. When this happens, the game doesn't always handle it correctly right away. It is possible to end up with a situation where two (or more) villages overlap and are still treated as separate villages. Villages can also overlap if the removal of a door shifts the center point closer to the other village. Tango Tek took advantage of this behavior to design several "overpowered" iron farms that tricked the game into overlapping several villages in a small space so they each could spawn golems individually.

The same thing can happen in reverse: if houses are removed from the center of a large village, the remaining ones may constitute two separate, smaller villages whose radii do not overlap, but the game may still treat them as a single, large village. Or, likewise, additional houses may shift the center point away from the furthest houses so they should not be included in the village yet still are.

When the placing or removal of blocks causes what-was-once-a-house to become no-longer-a-house, the game can fail to update this as well and still treat the door as if it should count as a house. Relogging used to fix this issue, reevaluating the village from scratch when you came back, but now, since 1.4 and later, the village is saved to the world file and so simply relogging does not cause a reevaluation. You will actually have to bust out and replace the door itself (or use the fix below) for it to stop being counted as a "house."

In all three circumstances, the fix is rather simple. Just walk, ride, fly, or boat far enough away that the chunks are unloaded from memory (a bit past your render distance, and then wait for a bit), and this will cause a reevaluation upon your return, correctly identifying only whatever houses remain. If the village(s) are within your world's always-loaded spawn chunks, they will never get unloaded from memory while the overworld is loaded, and so the village never gets reevaluated no matter how far you run. In this case, you can hop into the nether or the end for a minute; after sixty seconds even the spawn chunks will be unloaded (unless another player or entity travels through the portal in that time, which is how Tango Tek kept his creations from breakin every time you left the overworld.)

--------------------

A word on "roof" blocks:

It seems there are two kinds of transparent blocks. There are fully transparent blocks such as glass, torches, and fences, and then there are what I call "partially transparent" blocks such as slabs, stairs, and leaves, which are treated as transparent by the rendering engine (since they don't fill up the entire block space -- you can see through to what's behind them, so the game has to know to draw that part of the world anyway, even though there's a block between you and it. It knows to do this because the block that's in the way is flagged as a "transparent" block), yet they still block light from passing through (at least partially, as is the case with leaves or water), so they're still somehow considered opaque to the lighting engine, which appears to be where it counts. These partially transparent blocks will block the sunlight, and so will count as roof blocks. Fully transparent blocks still do not count. Water and lava (both flowing and source blocks) are partially transparent, and will count as roof blocks. Leaves count as roof blocks. Slabs and stairs count as roof blocks (and they don't even have to be upside-down.) I haven't tested every single block type so I don't have a full list of what does and does not count, but I know that torches don't count, fences don't count, chests don't count. The list goes on...

--------------------

The infamous "facing doors" myth:

There is a rumor going around, that two doors facing within a certain distance of each other will somehow cancel each other out, and neither one of them (or sometimes only one, depending on who you hear it from) will count as "houses." This is not a thing! It is nothing more than a misconception, a rumor, brought about by a misinterpretation of the significance of a particular image posted by Marfagames, who did much of the initial testing on villager houses, and the meaning of his caption:

Quote from Marfagames

And here left are 0 houses and the right 2 are 2 houses. The doors on the left get not negated through the other door, but through the one "roof" tile only in the range of 5 left and right from it.
[The original image is no longer available, but it looked something like this]:[INSERT IMAGE HERE -- coming soon!]

Let's take another look at what he wrote there: And here left are 0 houses and the right 2 are 2 houses. That's true, the two doors on the left do not count as houses, and the two on the right, do. But then look at what he says immediately after that: The doors on the left get not negated through the other door, but through the one "roof" tile only in the range of 5 left and right from it.

Marfagames' english is a little rusty, but what he is saying is basically this: The reason the doors on the left do not count as houses is NOT because they are facing each other, but rather it is because each one has exactly one space covered by a roof block on either side. So as you can see, even he said from the very beginning that it has nothing to do with the fact that they are facing each other! However, somewhere along the line, someone misinterpreted this to mean that facing doors somehow cancel each other out, and then everyone else took that rumor and ran off with it. If anyone ever tells you that facing doors will cancel each other out, you can send them here to get set straight.

Here is an image that demonstrates the overlap between the areas checked for roof blocks by each of the two doors. The door on the left checks above the pink blocks, and the door on the right checks above the blue ones (but only in the center row that's inline with the doors, of course -- additional wool to the near and far sides is just for clarity of demonstration.) Purple blocks represent the area where the two zones overlap, and these spaces are checked by both doors. Doors themselves are transparent and do not count as "roof blocks" for the other door:

Fig. 18

So looking at the blue door only, it has one covered space on the left side, and one also on the right:

Fig. 19

And likewise with the pink door:

Fig. 20

(Rotated 180°, viewed from the "far side" versus other images)

Since these doors both have the same number of covered spaces on either side, they don't have an "inside" or an "outside," and therefore can't be called "houses." However If you put additional blocks behind these (or just move the existing blocks back by one space, that would have the same net effect) then these additional blocks will be six blocks away from the far door, too far to be counted, but are still within range of the nearer door, creating the imbalance necessary to call them "houses":

Fig. 21

With these additional blocks in place, the doors now are valid houses. This is my understanding, and the Village Info mod agrees!:

Fig. 22

--------------------



SECTION 2: BREEDING AND POPULATION CAP

...or "How is babby formed?" A village's population is capped at a certain amount, based on available housing. Villagers will breed, provided there are at least two to begin with, until the number of villagers reaches but does not exceed 0.35 times the number of "houses" (defined above.) Previously, all that was needed to get villagers to breed was to provide them with enough houses. Since version 1.8, however, in addition to having enough housing to support the population cap, villagers must also be made "willing" to breed. Willing members of a village which has not yet reached its population cap will occasionally go in and out of "breeding mode" (indicated by animated heart particles above their head) at irregular intervals until two of them come together and produce an offspring in the same block space as one of the parents. This new villager will be assigned a random profession (indicated by the style and color of its clothing,) not necessarily the same as either parent. Like farm animals, the new baby will grow into an adult after exactly twenty minutes, and also like animals, villager parents have a five-minute "cooldown" period before they can enter breeding mode again (although I believe they can still be made willing again immediately, it just won't do anything until the five-minute cooldown has elapsed.)

**The wiki used to state that "once the cap is reached, any remaining baby villagers will grow to adulthood, but no new babies will be born, bringing the total population to somewhere slightly above the actual population cap," indicating that only adult villagers are counted towards the cap. I have not seen any evidence of this, and all my testing indicates that baby villagers are counted just the same as adults are. As soon as that last baby is born, all "love mode" animations cease to occur; killing either a baby or adult villager at that point will cause them to start up again.

--------------------

Killing villagers:

If a villager from a village dies to a non-player, non-mob source (i.e., environmental damage like fire, lava, drowning, cactus, suffocation, or fall damage) within sixteen blocks of a player, or if a monster kills a villager at any distance from the player, no villager in that village will be able to breed for the next three minutes. Further deaths within this time will reset the clock, not add to it. Breeding may resume three minutes after the last villager has died this way.

If a player attacks or kills a villager directly, it will affect their reputation in the village (see Iron Golem section, below), but it will not affect breeding.

--------------------

Curing zombie villagers:

Breeding requires at least two villagers to begin with. If you are starting a village from scratch, or if yours was wiped out by zombies and there are no villagers left (or only one), then the only ways to acquire more are hauling them in from another village (such as by boat, minecart, or nether tunnels), curing infected zombie villagers, or to cheat them in using creative mode spawn eggs.

To cure an infected zombie villager, you need a splash potion of weakness, and a golden apple. When you find a zombie villager, toss the potion of weakness at it, and then right-click it with the golden apple. The zombie will make a loud sizzling sound, emit orange particles, and begin to shake violently. It takes a couple of minutes for them to convert, so go ahead and trap him somewhere, and make sure he won't burn in the sunlight. After a few minutes, he will turn into a regular villager, at which point you can let him out to roam the village or do whatever.

Finding zombie villagers in the first place shouldn't be all that difficult. Each zombie has a 5% (1/20) chance to be a villager zombie instead, so it shouldn't take you too long (only about forty zombies, total) to find two of them you can cure back into villagers and get the population booming by more..."natural" means. Additionally, when a villager is attacked by a zombie (any zombie) there is a chance (based on difficulty: 0% on Easy, 50% on Normal, 100% on Hard) that they will turn into a villager zombie instead of just being killed.

--------------------

Infinite Breeding:

There is also a bug or glitch where sometimes the villagers will continue to breed indefinitely without regard to the population cap. Here's a quote from trunkz explaining how this works:

Quote from trunkz

[V]illagers need to be inside a sphere (radius = village radius) around the village center in order to breed. But the village counts only villagers that are inside a box (width, length = 2x village radius, height: 9 [always!]) around the village center. So with a sphere that can grow to any size, and a box that's always only 9 high, it should be apparent that there are some zones only covered by the sphere (above and below the village center).

You can simply reproduce/abuse this behavior by building 6 houses on the ground level (enough to set the villager limit to 2), drop 2 (or more) villagers into a 6 blocks deep hole, and leave one villager at the top to keep the houses "alive". The villagers in the hole will breed indefinitely, because they're not counted against the cap.

[images coming soon]

This nine blocks high is the same height as the range in which a villager can identify a house. I have not confirmed this, but perhaps these two are related -- that is to say that maybe a villager would be counted towards the cap if they are up to three blocks below or five blocks above (or exactly on) the level of the village center point.

--------------------

SECTION 3: TRADING

[coming soon]

--------------------


SECTION 4: IRON GOLEMS

...or "It's okay, he's with me." An iron golem's main purpose, "in-world," is to protect villagers from zombie sieges. In practice, they actually do a rather poor job at this, but it is also possible to "farm" them for the iron ingots they drop on death. Golems will roam the village and attack any hostile or neutral mobs they see except for creepers, wolves, polar bears, and llamas. They have extremely high health (100 points, or 50 hearts) and do not suffer fall or drowning damage. Their long arms can reach an enemy through a solid wall one block thick with a long-range melee attack that does not require line-of-sight and deals anywhere from 3.5 to 10.5 hearts of damage, or 7 to 21 half-heart "points" (on normal difficulty; 4-11 points on easy and 10-31 points on hard) as well as tossing enemies into the air, likely causing fall damage in addition to this.

When provoked by attacking them or a nearby villager, naturally-spawned golems will become hostile towards the player, moving toward the player whenever they are in sight and attacking whenever they are in range. They can sense an attack on a villager even without direct line-of-sight, they don't actually have to "see" it take place. Attacking one golem will not cause any other golems to become hostile, but attacking a single villager will bring the wrath of every golem within range (~12 blocks.) Running far enough away from a hostile golem will cause it to become neutral towards you again. Additionally, contact with water momentarily renders them passive -- they will not attack any players or mobs while standing in water and their neutrality towards players will be reset.

Iron golems will spawn naturally in a village of sufficient size, but can also be constructed in-world by the player, by placing four iron blocks in a T-shape (physically build it, not on a crafting table) and then placing a pumpkin or jack-o-lantern on top (the pumpkin/jack-o-lantern must be placed last, or else it won't work.) Player-created golems will never attack the player who made them, even when directly provoked.

--------------------

Reputation

Since 1.4, villages now track the "popularity" of players. Popularity is unique to each village/player pair, so one player can have different reputations in different villages, and different players can have different reputations in the same village. Popularity starts at zero for each player and is affected by their actions inside a village. Popularity is a numerical value that ranges from +10 to -30. If a player has a popularity of -15 or lower in a village, iron golems from that village will become hostile to the player without provocation. The following table shows what actions affect popularity, and by how much:

*(Note: this is an old image, when only trading a villager "for the last offer on their list" would update their trades, and was guaranteed to do so every time. Mechanics have changed since then so that now any trade has a chance to update their trades but is not usually guaranteed to do so. I find it likely, but have yet to confirm, that increasing reputation works the same way, so that a particular trade will always increase popularity [and update the villager's trades] the first time, and then have a 20% chance each time you perform that particular trade thereafter.)

--------------------

Golem farming:

Upon death, golems will drop 3-5 iron ingots and 0-2 poppies (formerly roses), which makes farming them a viable alternative or addition to caving or mining for your iron.

Golems will spawn near the center of a village if it has at least ten villagers (previously sixteen, before 1.4) and 21 houses. Additional houses beyond the 21st will make no difference as far as golem spawning is concerned, however, having additional villagers beyond the tenth will allow more golems to spawn, in increments of one golem for every ten villagers (so 0-9 villagers allows no golems to spawn, the cap is set at zero; 10-19 raises that cap to one, 20-29 raises it to two, etc.) This cap only limits the number of golems in a village at any one time; as soon as one is killed or leaves the village boundaries, a new one can spawn in its place immediately.

The golem spawning zone is a 6-high, 16x16-block area centered upon the village center point. As long as all the conditions are met (10 villagers, 21 houses, golem cap not reached,) then each game tick (1/20 of a second) there is a 1/7000 chance the game will try to spawn a golem. Basically it picks a random number between 0 and 6999, and if it picks 0, then up to ten attempts are made to spawn a golem. A random spot is chosen inside the spawning zone, and if that spot contains a solid block with at least 2x2 x4-high space above it (liquids are okay here -- golems can spawn in water, which is key to the iron farm designs linked below), then a golem is spawned there. [NOTE: For a long time, I had "3-high" written here. But it looks like that was incorrect, and while the golems themselves are only 3 blocks high, they actually need a four-high space to spawn in.]

This is repeated up to ten times or until a golem is spawned, whichever comes first. Then, the check is repeated each game tick, until enough golems have been spawned to reach the cap, at which point spawning is put on hold until either a golem is eliminated or the cap is raised. This means that, as long as the cap isn't reached, you can expect one golem spawn about every six minutes, on average, or roughly ten golems (30-50 ingots) per hour. Remember, though, that this is just an average, and the actual interval between spawns will necessarily vary to some degree. If you watch vigilantly, you will likely see spawns spaced much closer or farther apart than this six-minute average, but in the long run, it should all even out.

--------------------

Golem farming:

An iron farm is an artificial village in which golems are spawned and then funneled into a killing chamber where their drops can be collected. You can either hold the golems (outside of the village boundary, so more can continue to spawn in their place) until you come and kill them manually, or you can force them into cactus or lava to kill them immediately and use hoppers to collect the drops.

There are several ways to build an iron farm, but the most effective versions seem to be the ones that utilize two floors in the central golem-spawning zone, and keep all doors and villagers outside the zone, either above and below the center or in an outer "ring" on the same level. This is in order to maximize the number of available spaces for the golems to spawn in, which in turn will reduce the number of failed attempts, and keep the spawning rate as high as possible. This is much more effective than simply increasing the villager count to raise the golem cap, which only matters for the few seconds between the time when a golem spawns and when it is flushed out or killed, anyway. To further increase your output rate, you can build several separate "modules" and bring the golems or their drops to a central collection area. Since golems are immune to falling or drowning damage, the available killing methods are lava, cactus, or suffocation.

I have linked several iron farm tutorials at the end of this guide. Many of these creations were designed in earlier game versions so some of the details might be different (specifically, they often say you need sixteen villagers when now only ten are required, and they often have you start with minimal villagers and let them breed up to the required numbers based on the doors included in the farm, which now does not work unless you feed/trade with the villagers once they are in place.) Prior to version 1.8, MAGUS-APPROVED™ designs included those presented by trunkz, docm77, and MegaTrain. In my world I use a variation on the one from docm77's video but with only two pods of five villagers each instead of four pods of four (since you only need ten now instead of sixteen) and only 24 doors (since I bring them in from elsewhere, I don't need all the extra doors which were just there to facilitate breeding. Technically only 21 doors are needed but with 24 I still get the 4-way symmetry that puts the village center right smack in the middle of the structure.) I used to use one based on MegaTrain's MegaVillage concept, but since 1.8 that requires significant reworking to account for the new farming/willingness mechanic.

CSPerspective's videos detail earlier incarnations of the idea that do work, but fall short on efficiency in some of the areas I mentioned above. He also has a fourth iron farm video which does remedy these shortcomings, but I did not put a link to it as it's basically just a rehash of JL2579's design (from docm77's video, which I feel has a better presentation.) If you're going to follow the designs exactly, stick with docm77's or trunkz' video. If you want to design a farm yourself from the ground up, go ahead and watch them all to get some ideas.

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SECTION 5: ZOMBIE SIEGES

"...braaains!" At night, there is a chance that a zombie siege might occur. This is when a large number of zombies spawn in or near a village, attacking what villagers they can reach, crowding around and pounding on the doors of those they can't. On hard or hardcore mode, they can actually break down the wooden doors of the villagers' homes (this is true of all zombies, not just during sieges.) A zombie siege requires a village of at least 10 houses and at least 20 villagers. At midnight each night (18000 in Minecraft time), there is a 10% chance that a siege will be attempted that night. If a siege is to occur, attempts will be made each game tick until a siege is successfully initiated or the sun rises (technically, the attempt is abandoned when the sky light reaches level 12. Typically, this occurs at dawn although rain or thunderstorms can delay this brigtening since they reduce the light level significantly.)

For each player, the village with its center closest to the player is considered as a candidate village for a siege to occur if the player is within (radius + 1) of the village center; essentially, the player must be "inside" the village for a siege to occur. If the player is not within range of any village, the next player's village is considered. If the village has fewer than ten doors, fewer than twenty villagers, or has not been stable (no doors added or removed) for at least one second (20 game ticks), then the next player's village is considered.

Ten attempts are made to choose a starting point, on the y-height of the village center, at a random point on a circle with radius 0.9 times that of the village, that is not within the boundaries of any other village. If a valid starting point is found, a location is chosen as if to spawn a zombie there. If that check succeeds in finding a valid zombie spawning location, a siege is initiated at the siege starting point. Otherwise, the next player's village is considered.

Once a siege is initiated, up to twenty zombies may be spawned over the course of 2 seconds. For each zombie, up to ten attempts are made to randomly choose a spawning point within a 6-high, 16x16 zone centered on the siege starting point. If a valid spawning point is found, a zombie is spawned. During a siege, zombie spawns ignore player proximity, light levels, and other mobs, meaning even a well-lit and fortified village may suffer a siege. The best way to prevent them is to either keep your village small enough that they can't occur, or stay outside them at night.

SECTION 6: SOURCES AND ADDITIONAL INFO

I don't look at the game code myself, or anything. My info comes from in-game observations and the word of others. This is how it works, according to my understanding. I haven't included anything on trading in here yet, but for the time being, the wiki covers it pretty well. We also have a discussion going on over here about all the math and stuff behind how a villager's trade offers are generated.

We're all human (or most of us are, anyway) so there's always the chance that I have made a typo, or even that I am just plain wrong about something in here. If you see anything that you feel needs attention, please post it in this thread or shoot me a PM.

Sources: the wiki; trunkz' Village Info mod; various posts on these forums; and personal experience from building several different types of iron farm, from fixing up and expanding two NPC villages in my main survival world, creating my own villages from scratch, and from my own testing in creative mode.

Additional links:
- Marfagames' original post on village mechanics - Much of this information came from there initially, but it's a little hard to follow since everything is mixed in with discussion and scattered across over 500 posts on more than 20 pages, plus I think English is not his first language: http://www.minecraftforum.net/topic/1071744-
- Village Info mod by trunkz: http://www.minecraftforum.net/topic/1077712-
- Imgur gallery by Derrick - A briefer, more compact visualization of what makes a "house," and a bonus "villager breeding unit" that can support up to 35 villagers in an 11 x 10 or so space (the unit takes up that much space, the villagers themselves wander around outside of it, gettin' freaky in the daylight): http://imgur.com/a/xGhDP
- [Tutorial] Guide to Breeding Villagers in Minecraft - A video crash-course in villager breeding and housing presented by qmagnet:

- trunkz' iron golem farm tutorial video: http://www.minecraftforum.net/topic/1078108-
- Another iron golem farm design by JL2579 (tutorial video by docm77):

- MegaVillage: Manage 100+ villager trades + iron golem farm - A trading village with built-in iron farm (or vice versa) presented by MegaTrain: http://www.minecraftforum.net/topic/1762291-
- CSPerspective's iron farm:

- Minecraft Wiki page on NPC Villagers: http://www.minecraftwiki.net/wiki/Villager
- Minecraft WIki page on Villager Trading: http://www.minecraftwiki.net/wiki/Trading
- Minecraft Wiki page on Iron Golems: http://www.minecraftwiki.net/wiki/Iron_golem
- Minecraft WIki page on Zombie Sieges: http://www.minecraftwiki.net/wiki/Zombie_siege

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We're sharing sad stories? Here's one of mine:

Once I had a pig.
Then he died.
It was delicious, delicious murder.