Jewish forms of esotericism existed over 2,000 years ago. Ben Sira warns against it, saying: "You shall have no business with secret things". Nonetheless, mystical studies were undertaken and resulted in mystical literature. The first to appear within Judaism was the Apocalyptic literature of the second and first pre-Christian centuries and which contained elements that carried over to later Kabbalah. According to Josephus, such writings were in the possession of the Essenes and were jealously guarded by them against disclosure, for which they claimed a certain antiquity (see Philo, "De Vita Contemplativa," iii., and Hippolytus, "Refutation of all Heresies," ix. 27).