During a war between two rival colony worlds, each populated by humans genetically adapted to their own planet, combatants unearth a strange artifact that turns out to be packed with alien technology, and possibly alien life. A scientist studying it gives birth to quadruplets and then takes her own life, leaving the children's unexplained origin hanging over the rest of the war. As the fighting ends, the surviving quads grow into power over the hilldiggers — planet-scarring dreadnoughts capable of reshaping a world's surface.
Summary by Loreful, from public sources