Duelling is legal in the Empire only amongst nobles. There is a great deal of ceremony and structured law around duels and they are held as a sacred right. Most duels are fought for honour, though some are simply fought for the opportunity to kill an opposing noble.
Centuries ago, duels were common among all classes, before being outlawed as a barbaric practice. This caused more problems than it solved however as the resulting wars fought between competing barons threatened the stability of the Empire. A compromise was reached to allow duels to occur between the nobility only as a means of satisfying honour and preventing needless border skirmishes and minor wars.
Rules of duelling are as follows. Any noble may challenge another noble to a duel given a valid reason such as in insult to their honour or the honour of their family or liege lord. The challenged may choose the weapons of the duel. The challenger then chooses the terms of the duel, such as first blood, maiming, or a duel to the death. A duel must be fought within a fortnight of the challenge. Each noble must have a second to attend them during the duel. The duel must be overseen by a priest of a recognized deity. Nobles may name champions to fight on their behalf. These champions need not be nobles themselves.
In the Empire today, duels are typically fought by commoner champions rather than the nobles, and they are typically fought to the death for the entertainment of the nobles who go to great lengths to make a spectacle of the duels, making them more of a high class gladiator match rather than a means of satisfying personal honour.