Question: "What does it mean that the name of the demon was Legion?"
Answer: In Mark 5, Jesus visits the region of the Gerasenes and is immediately confronted by a demon-possessed man who lived among the tombs, cut himself with stones, and could not be kept in captivity (Mark 5:1–5). When Jesus asked the demon what its name was, the demon replied, “My name is Legion . . . for we are many” (verse 9).
In common usage, a legion was the largest unit in the Roman army. At that time, a legion averaged about 5,000 fighting men, though it could have thousands more or fewer. So the term legion refers to any large number of beings; a multitude. When the demon in Mark 5 said that its name was Legion, it meant that the demoniac of the Gerasenes was possessed by a large number of unclean spirits.
Scripture does not say exactly how many demons comprised the Legion within the man. However, when Jesus cast them out, they entered a herd of pigs feeding nearby. Legion caused the pigs to rush down a hillside and into the sea, where they were all drowned (Mark 5:13). The number of pigs killed was “about two thousand.” That detail suggests that Legion was composed of about two thousand demons. The large number of demons may account for the afflicted man’s untamable nature and great strength—strength that was no match for God, of course.
There is one other mention of a “legion” in the context of spirit beings, this time of good angels. When Jesus was being arrested, Peter pulled out a sword and wounded a nearby member of the mob. Jesus healed the wound (Matthew 26:51) and told Peter to put away his sword. The Lord reminded Peter that, if He needed help, He could have God send “more than twelve legions of angels” (verse 53). That might total 60,000 angels, but the exact number wasn’t the point Jesus was making. Rather, it was to remind the terrified disciples that God is always in control of all circumstances, even during the horrible injustice of the murder of His own Son.
It is interesting that the Bible refers to both holy angels and demons as forming legions. Legion is a military term, one that fits the Bible’s descriptions of spiritual warfare in several places (Daniel 10:13; Ephesians 6:12; Revelation 12:7).
How can we stand against such numerous and powerful foes? God completely equips believers for battle against satanic forces: “Put on the full armor of God, so that when the day of evil comes, you may be able to stand your ground” (Ephesians 6:13). As Christians, we are “more than conquerors” through Christ (Romans 8:37). Jesus is our Commander. He is the One who dispatched the demons named Legion with just a word. He it is who will some day throw Legion and all the other demons “into the eternal fire prepared for the devil and his angels” (Matthew 25:41; cf. Revelation 20:10).