The Essenes (es'-eenz) were followers of a religious way of living in Judaism that flourished from the 2nd century BC to the 1st century AD. Many scholars today argue that there were a number of separate but related groups that had in common mystic, eschatological, messianic, and ascetic beliefs that were referred to as the "Essenes". There are also contemporary movements which identify themselves as Essenes, including the "Orthodox" Christian Essenes.
The main source of information about the life and belief of Essenes is the detailed account contained in a work of the 1st century Jewish historiographer Josephus entitled The Jewish War written about 73-75 CE (War 2.119-161) and his shorter description in his Antiquities finished some 20 years later (Ant. 18.11 & 18-22). Claiming first hand knowledge (Life §§10-11), he refers to them by the name Essenoi and lists them as the followers of one of the three "choices" in "Jewish Philosophy'" (War 2.119) alongside the Pharisees and the Sadducees. The only other known contemporary accounts about the Essenes are two similarly detailed ones by the Jewish philosopher Philo (fl. c. 20 BCE - c. 54 CE; Quod Omnis Probus Liber Sit XII.75-87, and the excerpt from his Hypothetica 11.1-18 preserved by Eusebius, Praep. Evang. Bk VIII), who, however, admits to not being quite certain of the Greek form of their name that he recalls as Essaioi (Quod Omn. Prob. XII.75), and the brief reference to them by the Roman equestrian Pliny the Elder (fl. 23 CE - 79 CE; Natural History, Bk 5.73).
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