...in the years before the Great Flood, heaven dispatched a fleet of two hundred angels called Watchers to monitor the activities of creation. The chief Watcher was named Semjaza.
One afternoon, in the era of Jared, when the Watchers were stationed on Mount Hermon, Semjaza saw a woman bathing in a lake, her brown hair twisting around her. He called the Watchers to the edge of the mountain, and together the majestic beings looked upon the woman. According to numerous doctrinal sources, it was then that Semjaza suggested the Watchers choose wives from among the children of men.After some time children were born to the Watchers and their wives. These creatures were called Nephilim.