Jesus permitted the unclean spirits to enter a herd of pigs, and the herd rushed into the sea and drowned (Mark 5:12–13). Mark identifies the spirits as “Legion” because they were many (Mark 5:9).
In Mark 5:8–13, Jesus is already commanding an “unclean spirit” to leave a man. He then asks the spirit’s name, and the reply “Legion” signals a large number. The spirits urgently plead not to be forced away from the region, and they request permission to enter a nearby herd of pigs. This episode sits inside Mark’s larger sequence of power-filled scenes after the crossing of the lake. Immediately before, Jesus stills a violent storm, and then he meets the man in the tombs (Mark 5:1–7).
Mark presents Jesus as already in control before the negotiation starts: he is commanding an “unclean spirit” to leave the man (verse 8). The following exchange is not a contest of equal powers. The spirits speak as if Jesus’ decision determines what happens next—where they may or may not go (verses 10–13).
A careful answer keeps the immediate passage, the book's argument, and the whole-Bible storyline together, so the question is answered in context instead of as a detached idea.
Start with Mark 5:12-13, then read the surrounding section so the answer stays connected to the passage's flow.
12All the demons begged him, saying, "Send us into the pigs, that we may enter into them."
13At once Jesus gave them permission. The unclean spirits came out, and entered into the pigs. The herd of about two thousand rushed down the steep bank into the sea, and they were drowned in the sea.