- For catapults and ballistae, see Siege engine.
Sieges are large scale assaults on your fortress by other civilizations, normally goblins and necromancers. They are usually announced with the message screen "A vile force of darkness has arrived!" (the message screen differs depending on the attacking race : the previous one is for goblins), and the main screen shows the "SIEGE" tag along the top for the duration.
Caravans will not arrive at a besieged fortress. They will arrive, though, if a siege is broken quickly enough, but it is possible to miss out entirely on a civilization's caravan for the year this way. Even if they do arrive before the siege, the attackers may kill them or chase them off if they can reach them. Consider this when deciding how you set up your trade depot and how heavily reliant your economy is on imported goods.
A civilization will be unable to lay siege if it can't reach your fortress site, meaning you'll never get sieges if you embark on an island or in a valley which is completely surrounded by mountains. If you want to make sure that a certain civilization will be capable of laying siege to you, then look at the "neighbors" view of the Embark site finder when selecting your fortress site.
 Structure of a siege
- Siege forces usually consist of several 'squads'. Using the goblins as an example, each squad consists of several goblins of one military class (swordsman, lasher, etc.), and often one 'squad leader' (typically an Elite or better, which need not be the same class as the squad it leads).
- Occasionally, a squad will be mounted - this means each of its members will be riding a suitable creature, though the creatures typically vary between members. The squad leader can be mounted, even if his squad is not. These mounts can change the combat dynamics, since some can fly, are building destroyers, or have substantially different combat traits than their rider. For more info on mounted units, and the Fun they can unleash upon an ill-prepared defender, see: Mount
- After being sufficiently "successful" at defending against the siege (killing sufficient attackers, waiting them out, or some combination thereof), the attackers will retreat. All of the remaining squads and groups will head for the map edges and leave, typically favoring the edge they entered from. Once all of the remaining attackers have decided to retreat, the "SIEGE" tag will go away.
- It is possible to have multiple sieges at the same time. If the attacking civilizations are at war with each other, they will start to fight with each other as well.
- Different races will favor different styles of attack during sieges. The following attack styles were observed in .40d; it remains to be seen if these traits are still present in current releases.
- You can turn off sieges and Forgotten beasts altogether by editing the d_init.txt file to change [INVADERS:YES] to [INVADERS:NO].
Goblin sieges are announced with the message, "A vile force of darkness has arrived!"
Goblins will start laying siege to your fortress when you reach a certain population, usually around 80. Usually the tactics used by the goblins are no more sophisticated than charging in an open march toward your fortress and attempting to kill your dwarves. Goblins sieges often include groups of Trolls, Ogres, or Cave dragons that can break buildings and smash workshops. Unlike the squads, however, these 'groups' usually enter the map in single file, somewhat akin to arriving migrants. These war creatures usually possess random civilian classes, and show little of the organized behavior of the squads. Goblins may also bring elite human or even dwarven fighters as leaders of their squads, previously kidnapped by snatchers. Goblin sieges usually involve mounted squads, some of which can fly over whatever defenses you might have set up to stop them.
Elven sieges are announced with the message, "The elves have brought the full forces of their lands against you."
It is possible to have elven attacks as well, but that usually requires some effort on part of the player, or for your starting civilization to have a pre-existing conflict with a nearby elven one. You can check this when you embark while looking at nearby civilizations, where it will read WAR next to the elf civilization, though it seems to be entirely dependent on how world gen plays out and embarking at a time when a war is happening. Another, possibly simpler (and more amusing) way to elven siege is to blatantly provoke them. If you don't want to be attacked by elves you should not offer them wooden goods or goods stored in wooden barrels or bins. You might also avoid clearing too much woodland, as elves will be offended if you do so. Elves use stealth squads, a la goblin ambushes, to hide their numbers and locations.Verify It should be noted, however, that unlike goblin ambushes which cap at four squads, elves can come in vast numbers, atop mighty (and tasty) unicorns or other exotic beasts. Fortunately, unlike goblins and humans, who wear heavy armor and wield metal weapons that can cause considerable damage, elves fight with flimsy wooden swords, and march into battle wearing wooden armor, or nothing but cloth robes and trousers. That isn't to say the attack should be taken lightly, because their melee forces aren't what you should be worrying about, as their bowmen are still deadly and can perforate your dwarves with hails of arrows in very short order.
Human sieges are announced with the message "The enemy have come and are laying siege to the fortress.".
Humans may also siege you should you let their diplomat die while visiting your fortress, if too many of their trade wagons get destroyed or if you trade with an elven nation the humans are at war with. Humans would sometimes set up a camp near the map edge they arrived on, harassing wandering dwarves and waiting for you to come to them instead of blindly charging toward your fortress. Humans often ride rather mundane animals, such as horses, camels (of both varieties), or war grizzly bears, and may bring along further war animals like trained cheetahs. Be aware that human siegers know of all traps that their diplomats have seen before, even their war animals are immune to those traps. If you had a human diplomat in your fort, best assume that your traps are useless against the invaders unless they were built after his last visit. A removed and rebuilt trap counts as "new", even if it's the same type of trap in the same tile.
 Necromancer sieges
Necromancer sieges are announced with "The dead walk. Hide while you still can!"
Necromancers will besiege your fortress by sending undead to your fort or even coming themselves. Either way, undead sieges are a guaranteed source of Fun. The undead units will arrive from all sides of the map in huge numbers, and begin slowly meandering towards your fortress. It is recommended that you have
many traps every single trap you could possibly build set in advance, and when the undead legions arrive, lock everything down. Be sure to lock down all of your butcher's shops, crypts, and refuse stockpiles, as necromancers can reanimate armies of body parts to destroy your fortress from the inside. Also, be careful with fishery workshops, as reports of mussel shells rising from the dead are fairly common. Necromancers will raise any corpse or corpse part that they see, and simple proximity to undead can cause things like skin and hair to rise and attack the unfortunate butcher. Undead sieges may arrive with as few as one zombie to as many as one hundred or more. It doesn't really matter how many arrive; if you are not prepared, you will probably get slaughtered, as one zombie can easily become two zombies, then four, then eight and so on. If the zombies cannot get at your dwarves immediately, they will simply mill about on the surface until something living (wild animals included) comes too close or until they are all destroyed. Like other sieges, it is also possible to wait out necromancer sieges, though this can take a year or more. Necromancers can besiege your fortress at any time, including before the second spring's elven caravan arrives, or even before the first dwarven caravan arrives in the fall of your first year (thus preventing its arrival). The number of undead sent will depend on your wealth and population, and early sieges tend to have as few as 3 undead; but can cause very much cheesy fun if a lone necromancer accompanies them (which isn't uncommon).
- Enemy squads will never abandon their caged or dead leader. Bug:1598
- Amphibian invader mounts drown their riders. Bug:926
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