The first part of the Book of Enoch describes the fall of the Watchers, the angels who fathered the angel-human hybrids called Nephilim.
Nickelsburg writes that "1 Enoch is a collection of Jewish apocalyptic traditions that date from the last three centuries before the common era". And that the dating of the various sections spans from early pre-Maccabean to 160AD.
Various Aramaic fragments found in the Dead Sea Scrolls, as well as Koine Greek and Latin fragments, are proof that the Book of Enoch was known by Jews and early Near Eastern Christians. The older sections (mainly in the Book of the Watchers) of the text are estimated to date from about 300–200 BC, and the latest part (Book of Parables) probably to 100 BC.
Enoch contains unique material on the origins of demons and Nephilim, why some angels fell from heaven, an explanation of why the Genesis flood was morally necessary, and prophetic exposition of the thousand-year reign of the Messiah. The Book of Enoch (also 1 Enoch Ge'ez: መጽሐፈ ሄኖክ, maṣḥafa hēnok) is an ancient Hebrew apocalyptic religious text, ascribed by tradition to Enoch, the great-grandfather of Noah.