From Solium Infernum Wiki
There are five named ranks: Prince, Duke, Marquis, Baron, and Lord. It is possible that during the game your rank will increase to a level beyond Prince, but you will continue to be called a Prince and there is no in game way to determine your true value other than manual calculation.
You pick a rank when creating your avatar (at a cost of 3 points per rank above Lord).
Effects of Rank
Your stronghold will have a level of rank+1.
Your stronghold attributes will sum to rank+6.
You will get rank (or rank+1) tribute offerings on the first turn of the game. The +1 offering is random, apparently a coin-flip.
Becoming a Blood Lord will increase your rank by 1.
Becoming a Blood Vassal will set your rank down to the minimum (Lord).
Your infernal rank versus that of your fellow competitors for the infernal throne will have a significant impact on diplomacy over the course of the game. Generally speaking, lower ranked players will have a hard time dealing with higher ranked opponents in the following ways:
- A greater delay between diplomatic actions. Between equally ranked archfiends, the usual delay between demands is two turns. Between a Lord and a Duke, it may be four turns.
- Ground wars will have higher requirements. A Lord wishing to declare vendetta on a Duke may need to capture at least three Places of Power in four turns (exceedingly tricky), whereas in the reversed situation the Duke will probably be able to set an objective of just one.
- Demands for tribute must begin at smaller values. Equally ranked players may initially demand three tribute cards from an opponent, a low-ranked player can usually only demand a paltry single tribute card from a vastly higher ranked opponent.
- In the event of a tie when bidding on something in the infernal bazaar, the higher-ranked player will win.
- Some events reference one's infernal rank.
Prince of Hell
Rank value: 5
As a Prince of Hell you are a member of the elite and you hold great sway in the decisions of the Infernal Conclave. All others are irritating imps snapping at your heels, and the Throne is your right by spiritual aptitude, if not by position.
Duke of Hell
Rank value: 4
As a Duke of Hell you have substantial influence in the Infernal Conclave. You consider those below you future vassals or grist for your ambitions. Those above you will soon recognize the merit of your claims on the Infernal Throne.
Marquis of Hell
Rank value: 3
As a Marquis of Hell you hold marginal influence in the Infernal Conclave. You recognize that you will need to work hard to subvert your superiors' claims and assert yourself to the Throne, but beware: two sides often make enemies of those who occupy the middle.
Baron of Hell
Rank value: 2
As a Baron of Hell you have some small influence in the Infernal Conclave but you have the will to greater power. Soon those fops in the Conclave will fear you and submit to your claim to the Infernal Throne, ensuring that it is awarded by merit and not some inherent yet tangential right.
Lord of Hell
Rank value: 1
As a Lord of Hell your have little influence in the Infernal Conclave but to reign is worth ambition.