Zombie siege



Sieges were introduced in Minecraft 1.2.1. While zombies will naturally spawn in low light levels, a siege is a special spawning of many zombies at night regardless of how well lit or walled off the village is.

Usually, a whole mob of zombies will concentrate on one door or villager, and will break a wooden door down in hard/hardcore, entering the building. This causes the villagers to flee and get attacked by the zombies on their way out.

Defense
Villagers will enter their house and slam the door before the zombie can get in, but they do not attack.

Iron Golems defend Villagers from Zombies and other mobs during such attacks and all other times, and can naturally spawn in a 16x16x16 area around the center of the larger villages.

Surrounding your village with a wall and lighting it are staple defenses for the normal mob spawns, especially creepers. However, they are ineffective for sieges because the zombies can spawn inside even a well-lit village. Zombies may prefer to spawn outside of the village or in the dark when given an access route. If this is true, a great defense would be a piston drawbridge (triggered by a pressure plate) that connects to a dark area outside of town.

Wolves and Snow Golems may also be stationed to keep the horde at bay, however Snow Golems will be useless in a desert village due to damage incurred from the biome, and the latter carry the risk of causing friendly fire with the Iron Golems. The former are also easy to maintain due to the large quantity of Rotten Flesh that a horde will yield when defeated.

Hard mode: All doors should be one block above the ground. This still allows villagers to enter but prevents zombies from breaking in.

Recovery
Villagers repopulate if there is open space in the NPC Village. This means that Villagers can recover from sieges by having children to repopulate the NPC Village, provided there are at least two Villagers and enough space in the NPC Village. Player-made houses can also cause Villagers to repopulate, as long as it is within the NPC Village, has a Wooden Door, and has a 3x3 space inside.

Iron Golems lost in the siege will eventually respawn if the NPC Village has at least 16 Villagers, or can be manually rebuilt by the Player.

History
On June 10th, 2009, Notch promised to have an expansion pack for Zombie Siege, but never achieved it. The first part of the project was added in Snapshot 12w07b by Jon.

As of Weekly Snapshot 12w07b, Villagers repopulate if there is open space in the NPC Village.

In Snapshot 12w08a, Iron Golems were released to specifically protect Villagers against attacks such as a Zombie siege.

Trivia

 * When a Zombie is attacking a Villager or door, it will usually ignore the Player unless the player attacks it.
 * Zombies also attack Villager children.
 * Although Zombies are the only mob that attacks Villagers, Iron Golems still attack other hostile or neutral mobs. This is probably because they can be created by The Player for self-defense, not for defending a village; it could also mean that other mobs may lead sieges against villages.
 * Amusingly, in creative, if you spawn a lot of zombies, they will eventually start a siege and all crowd one door.
 * Zombie sieges are more common when returning from the Nether and entering in a loaded game.
 * Lighting won't stop spawns. (Confirmed, both for lone Zombie sightings and the same Roughly 15 seen as of Snapshot 12w22a within basically the same small on-screen area).
 * Sieges can happen in player-made villages.
 * Sieges can happen in Mushroom Biomes, despite zombies not spawning there naturally, this is further evidence that the siege is "special".
 * In 12w32a, if you turn mob spawning off with "/gamerule", sieges can still occur.