The lands of Horiza are quite empty, but there are still a number of sites which definitively hint that a civilization used to exist here. How long ago this was, and perhaps more importantly, why they all vanished or died out is yet to be decided on. Studying this question is the Forgotten Dawn Society, as well as many other unaffiliated explorers and academics that are sponsored by or request travel into Horiza from the Horizan Guild Association.
There are painted maps left behind which indicate the precurs were aware of Leylines.