The Metal Monster by Abraham Merritt

The Metal Monster is an Abraham Merritt fantasy novel.Dr. Goodwin is on a botanical expedition in the Himalayas. There hemeets Dick Drake, the son of one of his old science acquaintances. They are witnesses of a strange aurora-like effect, but seemingly a deliberate one. As they go out to investigate, they meet Goodwin’s old friends Martin and Ruth Ventnor, brother and sister scientists. The two are besieged by Persians as Darius III led when Alexander of Macedon conquered them more than two thousand years ago.(Wikipedia)