I have a scenario in which the Kingdom of Aderia has King X of House Harranshield. A civil war to push the claim bannerman Y (of House Bloodshield) has on the throne (because his mother was the daughter of the former king) has been declared and a decade of bloodshed ensues. This decade of bloodshed ends when peace is signed and King X agrees to share the kingship with Y jointly and equally, and the two spend the rest of their reign consolidating the realm and repairing the damage the war caused.

Both X and Y's eldest son, still of different houses, now have an equally valid claim to the throne. When their father's died, rather than risk another civil war, they continued to share the Kingship. A law was put forward for royal approval by the small council advisors of both kings that required two kings in power at all times.

How might Aderia survive? It needs effective leadership to survive, but at the same time, I see issues rising;

Conflicts of Interest

Okay, so King X wants to do something with law W because it would benefit him. King Y says no. Who gets his way?


King X makes an alliance with neighboring Meralia and seals it by wedding his daughter to the heir of that country. However, King Y refuses to acknowledge that alliance because it puts King X's grandkids on the throne of Meralia in a couple generations.


King Y makes a trade deal with that neighboring merchant republic Aestoso. This deal harms King X's interests, however, and he refuses to abide by the conditions.

These are merely just some of the many possible problems that could arise. Now, I know you would say something like; "make a parliament". All this works fine in a country with relatively low crown authority, but I need Aderia to have unusually high crown authority.

So, keeping in mind political problems, can Aderia function with two equally-powerful kings?


The throne only passes on when both of the joint kings have died.

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    $\begingroup$ Inheritance: So there are two kings, and if one of them dies, the heir to the dead king can't become the new joint-king until the OTHER king also dies? So that means the living king is the sole king until he dies? Why wouldn't the heir be allowed to take the throne immediately? $\endgroup$
    – DMfiend
    Mar 9, 2016 at 17:22
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    $\begingroup$ What about the law of two kings at all times? If the inheritance point is valid you cant have that law, pass the law and you can end with a young and an old king together with all the problems of two different generations. What happens if one king has no sons, is a queen allowed? what if the king of one house marries the queen of the other house, and they have one son only? $\endgroup$ Mar 9, 2016 at 17:30
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    $\begingroup$ Why don't the kings simply join their Houses and let the firstborn son after the union inherit? $\endgroup$
    – Frostfyre
    Mar 9, 2016 at 17:33
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    $\begingroup$ This seems rather simple to me. ASSASINATION! If one king dies, and his son cannot take the throne until they both die, the lining King always gets his way. $\endgroup$ Mar 9, 2016 at 20:34
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    $\begingroup$ "The throne only passes on when both of the joint kings have died" - Sounds like you're inviting assassination attempts. Which tend to be a problem generally in most fictional medieval settings. But that rule will kick it up to 11. Maybe the death of one forces the abdication of the other, if there are two successors available, or promotes a temporary custodian to the second spot until such time, if not? $\endgroup$
    – aroth
    Mar 10, 2016 at 5:32

10 Answers 10


Wikipedia calls such an arrangement a Diarchy, and gives several examples, both historical and modern, of such arrangements, including the ancient Greek nation-state of Sparta for over 700 years, the Roman Republic, a few minor periods in England's history, as well as the modern Principality of Andorra. There's little detail on how these arrangements work in practice, but, at least in the cases of Sparta and Rome, it mentions that each has veto power over the other.

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    $\begingroup$ Ferdinand and Isabella of Spain is the most famous successful medieval diarchy that comes to mind. $\endgroup$
    – RobertF
    Mar 9, 2016 at 19:46
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    $\begingroup$ @RobertF Depends on the definition of "mediaeval". 1453 is the usual cut-off, with F&I thus being Renaissance rulers. Just being pedantic :) $\endgroup$
    – Nagora
    Mar 9, 2016 at 21:03
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    $\begingroup$ Worth pointing out that it was actually common place for European leaders to have a diarchic leadership relationship with their spouse going back as far as the Dark Ages (at least). And, yes, it frequently did cause conflicts when each monarch felt differently about a specific issue. So the famous example you cite is not an aberration, but an example of S.O.P. in European monarchies as far back as we have records. $\endgroup$ Mar 10, 2016 at 1:32
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    $\begingroup$ The reference to Sparta really helped. I will be modelling my system based off of theirs. Had no idea there was an actual term for this, though! $\endgroup$
    – Jax
    Mar 10, 2016 at 15:21
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    $\begingroup$ There's also Triumvirates and Tetrarchies that have been moderately successful. (A Triumvirate is different from a Triarchy in that the 3 rulers aren't actually kings, but otherwise shares many of the same traits. There don't appear to be any historical Triarchies to speak of.) $\endgroup$ Mar 10, 2016 at 16:20

Princes are responsible for finding a partner to rule with.

Inheriting the right to rule is not a simple process in Adeira. Because each king needs to be able to cooperate with the other king, and must reach what amounts to consensus agreements with the other king, simply choosing the first heir from both ruling families could easily result in ruler disputes that could tear the kingdom apart.

Instead, the princes, princesses, and other eligible potential rulers must find a partner to rule with if they want to take the joint throne. A partnership must have one individual from each ruling family to be considered. The partnership, together, will then present to the ruling kings their case as to why they should be considered to take the throne, after which the ruling kings must come to an agreement as to which partnerships they think would make good rulers. Only if both kings agree to a partnership can that partnership be considered a successor to the throne.

Successors are then granted a duchy to jointly rule, which they must do effectively to remain a potential heir. All potential heirs must be sorted by the sitting kings, although the kings can choose the manner in which such sorting is conducted. First among these is the crown partnership, which serve as dukes of the capitol until such a time as the ruling kings leave the throne, at which point they will appoint a new crown partnership and take the throne.

A partnership is only allowed to rule so long as both partners agree to it.

Naturally, a partnership which cannot abide itself cannot effectively rule. A partnership is dissolved should either partner become disillusioned with the quality of their running mate or die. Partners cannot be swapped out in a partnership, so if one (or both) of the partners wish to remain a potential candidate, they must find a new partner and go through the vetting process again.

This is true even for kings. The quality of one king is no indicator of his skill at navigating any potential future partnership, so if a king dies or otherwise decides to abdicate the throne, his partner also loses their place and the partnership is replaced by the crown partnership. A former king can, of course, find a new partner and be vetted for a dukedom. A former king can even potentially becoming part of a new ruling partnership in the future, and in the case of a king who was formerly a beloved ruler, there may be considerable pressure on the new monarchs to step down and allow the new partnership to rule, but this is by no means required. The new partnership has ever right under law to remain in control of Adeira until such a time as their partnership comes to an end.

The kings rule by consensus only.

The kings wield absolute power over the land, but only if they both agree to it. This belief has been enshrined in both the political sphere as well as in the spiritual one. Humans are seen as quarrelsome by nature, so if two kings can agree on a policy, this is seen as a clear sign that the policy is not an act of man bu an inspiration from above.

While the kings may, among themselves, decide to delegate responsibility to one another, perhaps with one king handling domestic affairs and one foreign, all of their decrees are theoretically made by consensus. Should either king oppose a decision, that decision is not made. Throne room argument and bargaining are common, with both kings often seeking favor for their house and relatives, but this requirement for consensus means that the kings will always present a common front on any decision they choose to turn into policy.

The only exception to this, of course, is in abdication. Any king can choose to remove himself from the throne at any time, dissolving his partnership and removing his former partner from the throne, as well. Of course, this means a considerable loss of personal power, so kings rarely choose to abdicate, sometimes going for years without speaking to one another due to bitterness from internal conflict, while still technically ruling as a member of a joint partnership.


Domains of Power

It's fairly common for two leaders to share power; historical conflicts between leaders are what led to the popular arrangements of executives/ministers/legislators/judges that we have today. You could allow each co-king to have their own domain: perhaps one governs internal affairs, the other external. Or one deals exclusively with learned trades (medicine, law, diplomacy, religion) while the other deals with common affairs (agriculture, tradesmen, military).

You Don't Need Absolutism

I'd also like to point out that medieval kingdoms had extensive power sharing relationships.

In the political sphere, a single powerful rules wasn't a common ideal until the end of the medieval period. A more typical medieval system involved several local and regional leaders sharing a piece of territory. This was the essence of feudalism: lower lords offer their support to regional leaders, who in turn pledge their own support*.

Power was also shared with other groups - trade guilds, the Church, aristocracy, and other groups were less "ruled" by the King, and more uneasy allies required to get work done. Your two kings could easily come from different factions who require each other to get work done.

One historic example that you could adapt: In the early medieval period in England, kings were selected by a council (not born into the position), and enforced their legitimacy with religion. Maybe one of your "kings" is the elected king, and the other is a religious leader. They each use their power to help the other out, but at times come into conflict.


Could it work? Sure. All the issues you bring up come down to, What happens when the two kings disagree? So yeah, there'd have to be some procedures in place to resolve that.

The Roman Republic was led by two consuls who shared power. Basically, the government could not act unless they both agreed. In extreme cases, the Senate would vote.

Saying they both have to agree, period, is probably impractical. At some point there will be an issue where you have to go one way or another. "Neither" may not be logically possible, or it may be a distinct third option, or it may be theoretically possible but not practical. Like, a neighboring kingdom has proposed an alliance. Should we accept their offer or not? We can't say that we'll neither accept nor reject. We have to do one or the other.

Of course "two" is an awkward number because any disagreement is a tie vote. If there were three kings, you could say that they take a vote and majority rules.

So you have to have a way to break ties. The most obvious possibility is to have some third party who is called in to decide in such cases. Perhaps some sort of senate or parliament, or the most senior member of the nobility, or whatever.

Perhaps you could say that king X has the final word in some areas and king Y in others. Like X gets to decide in foreign affairs and military matters, while Y decides in economic and domestic law questions. Or whatever division. That would have the catch that they might argue about which category a question falls in, and then you have the meta question of who has the final say on what category something is.

If the kings basically get along they might be able to resolve disagreements amicably. If one is more forceful and dominating they might end up in practice as being senior king and assistant king. Or they might constantly be at odds and there's an endless power struggle and they spend more time fighting each other than solving the country's problems.



This hasn't really been covered by the other answers, but it seems self evident to me. If one king's son cannot take the throne until they both die, then have one King kill the other. Then the living King always gets his way.


The main issue would be the one house accusing the other house of murder. This could potentially cause another civil war. And we don't want that.

So you have to use positions or somethi, and make it look like natural causes or a freak accident. That way, the one King is not held accountable for the other's death.

I recognize this is kind of cheating, but a King is used to getting what he wants.

Take Turns

One king's eldest son is the ruler, and the other king's son is his closest advisor. When the King dies, the eldest son of the advisor becomes the new King, while the eldest son of the dead King becomes his advisor. That way, it is always clear which King holds more clout in decisions.


Since the real problem is getting the two kings to agree "jointly and severally" on issues, you have essentially set up conditions for paralysis of the kingdom, or civil war.

To avoid this, the co kings could try several different setups:

  1. A King for domestic affairs and a King for foreign affairs. This might work if the two kings have different interests. The domestic King ensures domestic harmony, sets the laws of the kingdom and is the patron of arts and science (such as they are). The foreign affairs King is a diplomat, adventurer and, if necessary, the warlord of the kingdom. He is the one who visits other potentates, sponsors expeditions to other lands (think of Prince Henry the Navigator of Portugal) and leads the armies of the kingdom against foreign enemies. While there is some overlap (the domestic king raises taxes to pay for the overseas adventures and the army, and will have some say in foreign policy insofar as it affects domestic policy), the separation of the two domains with two specialist Kings means the ruler isn't overwhelmed by events at home and abroad. As well, there could be an age based succession, the new, younger King is the foreign affairs King, who movies to the domestic throne when the elder King dies, while recruiting a new foreign affairs King to replace him.

  2. The Nobility take over. Two Kings at loggerheads or with mutual veto powers is a recipe for disaster. Rather than allow the kingdom to descend into anarchy, the Nobility create a body which advises the Kings and has the right to "direct" them. The Noble houses have the high cards here, since they collectively have more wealth and manpower than the Kings either individually or collectively, so can impose their will on the Kings if needed. The Noble houses also enforce their will by vetting the selection of new Kings to replace the old, either those who die or those forced to abdicate. This is not ideal either, as clever Kings and ambitious nobles could conspire to empower one faction over the other. As well, the most likely outcome is a replacement of Kings with puppet Kings who are figureheads for the nobility, somewhat like feudal Japan's Emperor was a figurehead for the Shogunate.

  3. Reversion to the lower energy state. Having two "co Kings" is expensive in terms of time and resources, so there will be a great deal of pressure to eliminate this system at some point. Either this gets sorted violently (assassination, civil war), by inertia (one royal house has no suitable heir, so no one bothers to find a replacement), or agreement (the one royal house has a princess rather than a prince, so the houses are joined in marriage), but in the end, there is only one King left on the throne.


As AndreiROM pointed out, you can't split Absolute Power. Either you have it or you don't.

However, making a truce between the two kings is a first step. They would each have their own kingdom. By making themselves close allies it would start merging the two countries together. Especially if they come to each others aid.

Now for the future, each one can provide a child for a union to unite both houses, this was a common practice to cement alliances and make allies. Eventually the union would produce an heir who would be of both houses and be able to rule both countries as one individual.

  • $\begingroup$ Which technically correct if trying to build a world where the kingdom has two rulers this doesn't help. $\endgroup$
    – Tim B
    Mar 10, 2016 at 13:26
  • $\begingroup$ @TimB I completely disagree. I stated how the most likely course would be for two absolute rulers to handle things for the near term and most likely for the long term. $\endgroup$
    – bowlturner
    Mar 10, 2016 at 13:58

I think the situation in Aderia would go to hell in a hand-basket sooner rather than later.

A King is by definition a ruler - typically by the grace of God, etc. What kings throughout history have in common is that they hold absolute power, and don't like being told "No". They are not democratically elected leaders with a finite term. They are not council members. In fact, the whole idea of democracy would sound ludicrous to them.

Two people cannot jointly wield absolute power. Look at how well it works out for UN to have Russia and the US both wield veto power.

Big decisions such as raising an army, military decisions, taxation, sentencing people to death, legislating religious rights, etc. have to be made firmly and decisively.

Having one ruler declare himself as the backer of military strategy X, and the other back military strategy Y would leave everyone in limbo - and have them sending assassins after one another in the middle of the night.

The role of the King in medieval society was to have someone who is ultimately responsible when things go to hell. When the nation is threatened, that person makes a decision. When the barbarians are a the gates that person leads the charge against them.

Having two former - bitter - enemies try and cooperate on such a scale is ridiculous. Just look at politics.

  • $\begingroup$ I think you mean the UN, not NATO. NATO was specifically created to counter the USSRs power during the cold war. $\endgroup$
    – James
    Mar 9, 2016 at 20:20
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    $\begingroup$ But isn't the OP asking for a way to make it work, not reasons why it won't? $\endgroup$ Mar 10, 2016 at 4:27
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    $\begingroup$ Almost no kings in history has had absolute power, especially not in medieval Europe. They have, almost exclusively, depended on the support of nobles and it is not unheard of that a powerful noble, under the king, was the de facto leader of the realm, leaving the king little more than a puppet. All kings (at least with anything beyond a single torp to rule) have had councils (sometimes even representing the population). It was not uncommon to have laws which forced the king to take up any complaints the local population had with their lords. $\endgroup$
    – Clearer
    Mar 10, 2016 at 12:48

As others have suggested, sharing power could lead to an even worse feud or to nothing at all being accomplished as each king vetoes the other.

Perhaps King X remains king in name while Y is named Supreme Consul/Head Priest/Knight Commander. Y exercises considerable political and military power but still ultimately owes loyalty to King X. If Y oversteps his bounds, then X issues some imperial mandate condemning the actions of Y. The lesser lords and ultimately the people are bound by faith and loyalty to obey King X. Though the kingship is largely reduced to a ceremonial position, X still has the ultimate authority and legitimizes Y's leadership. This would serve to pacify the loyalists who want the king to remain, while still allowing Y to wield power.
Another issue this solves is divine right. The King was often regarded as a mythic figure in medieval society, often acting as the agent of God. To defy the king would be to defy God. If a common man, even a member of a house of lords, were to unnaturally ascend to be king, it may weaken the kingship's hold of power over the people.

For historical examples, I am thinking something along the lines of the Emperor - Shogun of feudal Japan, or the Pope - Holy Roman Emperor.


I see a few scenarios where this might work out.


The two kings would likely forge a real alliance with each other, through marriage. This way only one, effective, family would be on the throne. Any pretender could have their claim stripped, legally, reducing the threat they would pose to the current throne. This won't eliminate such a threat, but it would make it harder for any would-be usurper to gain support.

Rule by Council

Rather than having the kings do the ruling, the effective rule is delegated to a council of some sort. This council could work much like a European monarchy, where the royal families are little more than (very privileged) centerpieces in society.

United we stand

Ruling a country is hard work and takes a lot of skill. By having someone else, who has exactly the same interests as you (ruling the country, keeping the vassals at bay, getting rich) you're pretty sure you also have someone you can trust. If you're alone, you could easily end up in a situation where you (think you) have nobody to trust.

Internal division

The realm could have an internal division, where the realm, externally, is still one realm. The different vassals within the realm, would only own fealty to one of the kings. This is what happened to Francia after Peppin died and Charles the Great and Carloman inherited Francia (it did not end well for Carloman). How the realm is governed internally could be in any fashion imaginable -- a formal alliance may be in effect, there may be a council where the kings have major influence or some other instrument.

The key point would be how laws are made and where they are in effect. In medieval Europe, it was far from uncommon to have different laws in the same country. As an example, Denmark once had Jyskelov, effective only in Jutland, while Skånske lov, was in effect in Scania (and perhaps Zealand). Given this, there may not even have to be consensus on how laws are made or which are in effect where, as long as it's clear who make the relevant decisions.


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