Enamour was a metal that looked like gold. It was green when semi-liquid. It was a natural emotional amplifier that made people desire it more than anything to the point of (sub)conscious cleptomania — stealing, in other words. It was created by a mechanical dragon.
They used it to get back at the city because they hated the Grand Council. Since Geath owned the country land on which the brothers lived, they were taken by the council members and forced into labour. When enamour was discovered in Geath, two races, the Bright Nobles and the Regulators, battled over it. (PROSE: The King's Dragon)