When the demon saw Jesus coming, he cried out, “What have I to do with you, Jesus, Son of the Most High God? I beg you, do not torment me!” (v 28). “Jesus asked him, ‘What is your name?’ And he said, ‘Legion.’ (For many demons had entered into him.)” (v 30).
The Greek word is λεγιών, which is a transliteration of the Latin legio, a foreign loan word. It refers to a Roman legion, which consisted of 5,000 – 6,000 soldiers. The word came to be used of a very large number.
λεγιών occurs three times in the New Testament, twice in connection with this story (Mk. 5:9, 15 [λεγιῶνα]) and once in Jesus’ assertion that the Father could “immediately place at my disposal more than twelve legions (δώδεκα λεγιῶνας) of angels” (Matt 26:53).