The Mark of Shadow first appeared among the elves of the Phiarlan line, and the house quickly turned the mark’s powers of shadow and illusion into an economic dynasty. The suspicion of their kin drove them from Aerenal to Khorvaire, and the house splintered during the Last War, giving rise to House Thuranni. The two houses of shadow control the business of espionage throughout Khorvaire, but they also operate more legitimate ventures related to art and entertainment.
Phiarlan blood still runs among some of the Aereni elves, and the Mark of Shadow appears once or twice in each elven generation. Elves bearing this mark are always inducted into the elite force of the Unknown — an espionage agency in the service of Aerenal’s Unknown.