Serpent's Skull in Eberron
Dragonmarks started appearing on the flesh of certain people around the time of the unification of Galifar. These marks, almost like tattoos, granted special magic power. Over the centuries, the Dragonmarked Houses have consolidated their power and built enormous commercial enterprises.
The thirteen Dragonmarked Houses collectively wield power on a continental scale and their services are available throughout Khorvaire; they are arguably the greatest power brokers in Eberron. Each house controls one or more powerful trades or commerce guilds and they do not hesitate to crush competitors.
The Dragonmarked Houses are also patrons of the arts, sponsors of scholarship and exploration, and innovators that have enhanced the lives of nearly all Khorvairians.