Polygamy (or polygyny, to be more precise) is a Muslim-exclusive marriage mechanic that allows Muslim men (including patricians) to marry multiple wives (up to a maximum of 4).
Polygamy allows Muslims to have a lot more legitimate children than Christians (assuming your wives are of child-bearing age). This is closely tied with decadence as it encourages a lot of sons who may become decadent, and whom you may need to give titles to. There is a first wife, who is your favorite among wives, who gives you the stat boosts. Secondary wives do not give stat boosts. However, they can become your spymaster.
Effects of Polygamy
If you as a Muslim do not marry enough wives, you will get a prestige penalty. Here's an overview of how many wives are expected at a certain rank:
- Count: 2
- Duke: 3
- King / Emperor: 4
These are expected minimums, not limits, although no more than four wives can be taken regardless of rank. In fact, rulers under polygamy traditions are encouraged to take as many wives as possible, meaning Muslim counts can take four wives if they feel like it, and will even get more prestige bonus for it.
Choosing the right wives
With open-agnatic succession, you can choose your heir by giving him titles, since the most powerful son will inherit. This allows for controlled breeding. You can easily get a genius as your successor when you marry only women with the Genius trait. You just have to search for them in the character finder.
Muslim succession is agnatic, so you will not be able to push your wives' claims. Your sons can inherit claims from them, however. Additionally, your sons will be eligible for inheritance when your father-in-law dies, because agnatic open succession considers both sons and grandsons.
You can form alliances with the relatives of all of your wives (and the relatives of all your sons' wives), not just your first wife. This makes it easier to arrange alliances between Muslim rulers, but may also entangle you in more allies' wars.
After the 2.5 patch (concurrent with Conclave) the new alliance mechanics with automatic, renewable non-aggression pacts upon marriage make marrying within the realm more attractive: a vassal cannot join or form a faction against his liege when he has a marriage pact with him, nor can the liege revoke an allied vassal's title. This can be very good for realm stability if you have a large number of vassals, such as the Umayyad and Abbasid dynasties in the early bookmarks.
Rivalry between wives
The first wife is a very prestigious title and the secondary wives will try to attain this status. They will sometimes ask you for the status of first wife, and if they are in a scheming mood, they might kill the present first wife.
Wives (who have sons) also like to see their offspring on the throne and might attempt to kill the current heir. They might even be bold enough to murder all sons but theirs. If you catch them in the act, you will have an option to execute or imprison them. Wives who are Ambitious , Envious , and/or Cruel are more likely to try to murder your other sons.
Age of Wives
There are some advantages in marrying at least 1 or 2 wives who are past child-bearing age (45). They give you extra prestige (or prevent prestige hits) and do not have the problem of killing the sons of other wives since they don't (and can't) have sons of their own. With your sons coming from one or two mothers, your heir is more likely to have full brothers (-20 opinion) rather than half-brothers (-40 opinion) as potential competitors.
- Marry the number of wives expected of your rank to prevent prestige hits.
- Marry more wives than is expected of you for prestige boosts.
- Women with good congenital traits should always be married.
- Wives will try to become first wife or kill your heir in favor of their son. Wives who don't bear children will have less incentive to plot against your heir.
- To control the number of children being born, consider marrying women near or past 45 years old (where fertility drops to 0). Your heir will also more likely have full-brothers rather than half-brothers as potential competitors.
- Muslim patricians can marry 4 fertile wives, but beware of intrigue within the family.
Pagans, Zoroastrians, followers of the Indian religions and all tribal rulers (including Christian and Jewish religions), rather than marrying multiple wives, may take up to three concubines.
Unlike secondary wives,
- a character can take a concubine without being married (This is useful if a wife of suitable status is unavailable, which would force you to take prestige hits),
- a character can set aside a concubine, facing only a -25(-50) opinion penalty from the woman set aside,
- at birth, children of concubines get the Child of consort trait that gives -1 Diplomacy, similar to bastards, but they take their place in the line of succession just like those of wives.
Rulers get a bonus to monthly Prestige for having "nubile concubines". Taking a concubine of high status (such as the daughter of a king or queen) gives +25 prestige per rank. Concubinage doesn't give rise to alliances.
A decent strategy is to marry politically and take concubines who have good genetic traits to produce heirs, to get good tutors for your children or to get a good spymaster (only for pagans). This is especially true of Zoroastrians: marrying a close relative gets you opinion bonuses with your Zoroastrian vassals, but also runs the risk of inbreeding, so having children with a concubine first, or marrying someone past childbearing age, lets you outbreed for healthy heirs.
Lovers may be taken as concubines at the start of affairs to prevent any problems with siring bastard children or relation penalties to legitimate wives.
Women who are prisoners can be forced to become concubines. The abducted woman will be very angry (-50 "abductor"), along with her family (-25 "abducted close relative") and, if she was married, her former husband (-25 "wife snatcher").
If set aside, such women will stay in the abductor's court, allowing them to be married off to courtiers (even matrilineally), although they will return home if their new husband dies. Marrying these captured concubines to your own children can enable alliances, even between rulers of different faith.