Also see definition of "Legion" in Word Study
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Legion
NET Glossary: a division of approximately 6,000 soldiers (10 cohorts) in the Roman army
Legion [EBD]
a regiment of the Roman army, the number of men composing which differed at different times. It originally consisted of three thousand men, but in the time of Christ consisted of six thousand, exclusive of horsemen, who were in number a tenth of the foot-men. The word is used (Matt. 26:53; Mark 5:9) to express simply a great multitude.
LEGION [SMITH]
the chief subdivision of the Roman army, containing about 6000 infantry, with a contingent of cavalry. The term does not occur in the Bible in its primary sense, but appears to have been adopted in order to express any large number, with the accessory ideas of order and subordination. (Matthew 26:53; Mark 5:9)Also see definition of "Legion" in Word Study