The War of the Mark
A testament to their power lay in the ruins beneath Sharn. Despite being heavily outnumbered, Lord Halas Tarkanan waged a long war, seizing Sharn and taking it as his capital. Finally, sheer numbers defeated him, and he and his wife (named the Lady of the Plague) released horrific magical forces, destroying much of Sharn and themselves. Only 500 years later was Sharn rebuilt. To this day, plague and death still remain below the city and children lie awake at night in fear from stories told about the ghost of the Plague Lady.
In the end, the coalition of Dragonmarked Houses was victorious. In the centuries following the war, the Dragonmarked Houses rose to become economic giants, while the power of Aberrant Dragonmarks was culled, becoming a mere shadow of their former power.
After more than a millenium of exaggerated tales and in light of the more recent horrors of the Last War, the old legends are losing their strength. The War of the Mark is a thing of the past, and hardly worth considering when there are so many other dangers on the continent of Khorvaire. However, the Aberrant Dragonmarks have become more frequent in recent years; their inherent powers stronger and more powerful much to the concern of the Twelve.