One of a series of three calamities that engulfed most of Arbre during the last decades of the Praxic Age and later came to be seen as precursors or warnings of the Terrible Events. The precise nature of the Harbingers is difficult to sort out because of destruction of records (many of which were stored on syntactic devices that later ceased functioning) but it is generally agreed that the First Harbinger was a worldwide outbreak of violent revolutions, the Second was a world war, and the Third was a genocide.